[docs] Fix SEO issues

docs/pages/blog/2020-q1-update.md

@@ -15,11 +15,11 @@ We have done eleven so far. We have optimized for stability.
 
 Here are the most significant improvements since the beginning of the year:
 
-- 🔍 We have polished the [Autocomplete](https://mui.com/components/autocomplete/) component (Combo box). We have closed more than [270](https://github.com/mui/material-ui/labels/lab%3A%20Autocomplete) issues and pull requests so far. We will promote the component to the core in the next major (v5).
+- 🔍 We have polished the [Autocomplete](https://mui.com/material-ui/react-autocomplete/) component (Combo box). We have closed more than [270](https://github.com/mui/material-ui/labels/lab%3A%20Autocomplete) issues and pull requests so far. We will promote the component to the core in the next major (v5).
 
   ![autocomplete](/static/blog/2020-q1-update/autocomplete.gif)
 
-  <p class="blog-description">useAutocomplete <a href="https://mui.com/components/autocomplete/#useautocomplete">hook</a> example, 4.5 kB gzipped.</p>
+  <p class="blog-description">useAutocomplete <a href="https://mui.com/material-ui/react-autocomplete/#useautocomplete">hook</a> example, 4.5 kB gzipped.</p>
 
   If you wish to make your first contribution to open source, the component has a couple of ["good first issues"](https://github.com/mui/material-ui/labels/lab%3A%20Autocomplete) that can be taken.
   If you have TypeScript expertise, the component could [benefit from it](https://github.com/mui/material-ui/issues?q=is%3Aopen+label%3A%22lab%3A+Autocomplete%22+label%3Atypescript).
@@ -28,15 +28,15 @@ Here are the most significant improvements since the beginning of the year:
 
   ![date picker](/static/blog/2020-q1-update/date-picker.png)
 
-- ⚠️ We have introduced a new [Alert](https://mui.com/components/alert/) component in the lab. While this component isn't mentioned in the Material Design guidelines, it's a common and well-established pattern. For instance, it can be interested when [combined](https://mui.com/components/snackbars/#notistack) with the Snackbar.
+- ⚠️ We have introduced a new [Alert](https://v4.mui.com/components/alert/) component in the lab. While this component isn't mentioned in the Material Design guidelines, it's a common and well-established pattern. For instance, it can be interested when [combined](https://v4.mui.com/components/snackbars/#notistack) with the Snackbar.
 
   <img src="/static/blog/2020-q1-update/alert.png" alt="alert" style="max-height: 369px; margin-bottom: 24px;" />
 
-- ⏭ We have introduced a new [Pagination](https://mui.com/components/pagination/) component.
+- ⏭ We have introduced a new [Pagination](https://v4.mui.com/components/pagination/) component.
 
   <img src="/static/blog/2020-q1-update/pagination.png" alt="pagination" style="max-height: 208px; margin-bottom: 8px;" />
 
-- 🦴 We have added a new "wave" animation to the [Skeleton](https://mui.com/components/skeleton/#animations) component.
+- 🦴 We have added a new "wave" animation to the [Skeleton](https://v4.mui.com/components/skeleton/#animations) component.
 
   <video autoplay muted loop style="max-height: 95px; margin-bottom: 24px;">
     <source src="/static/blog/2020-q1-update/skeleton.webm" type="video/webm" />

docs/pages/blog/2020-q2-update.md

@@ -16,7 +16,7 @@ Here are the most significant improvements since March 2020:
   The last 14 months have been spent focusing on improving the library under the v4.x development branch, while not introducing any breaking changes. During this period we have identified several important areas for improvement. While the absence of breaking changes is a significant time-saver for developers, it also limits the scope of the problems that can be solved and the quality of the solutions. We're excited about what comes next!<br /><br />
   You can find the documentation for the next version at https://mui.com/. The next 6-8 months will see weekly releases as always, following [the roadmap](https://github.com/mui/material-ui/issues/20012) and [milestone](https://github.com/mui/material-ui/milestone/35).
 
-- 📍 The icons package has been updated with changes made by Google, leading to [200+ new icons](https://mui.com/components/material-icons/).
+- 📍 The icons package has been updated with changes made by Google, leading to [200+ new icons](https://mui.com/material-ui/material-icons/).
 
   <img src="/static/blog/2020-q2-update/icons.png" alt="icons" style="width: 615px; margin-bottom: 24px;" />
 
@@ -26,7 +26,7 @@ Here are the most significant improvements since March 2020:
 
   Adobe XD and Framer support are also up for consideration if they attract a significant audience, but not until we've polished the Sketch and Figma assets.
 
-- 🔄 `LoadingButton` – [a new component in the lab](https://mui.com/components/buttons/#loading-buttons). This work is influenced by the [concurrent UI patterns](https://reactjs.org/docs/concurrent-mode-patterns.html) presented by the React team.
+- 🔄 `LoadingButton` – [a new component in the lab](https://mui.com/material-ui/react-button/#loading-button). This work is influenced by the [concurrent UI patterns](https://reactjs.org/docs/concurrent-mode-patterns.html) presented by the React team.
 
   <img src="/static/blog/2020-q2-update/loading.gif" alt="loading" style="margin-bottom: 24px;" />
 

docs/pages/blog/2020-q3-update.md

@@ -19,7 +19,7 @@ Here are the most significant improvements since June 2020. This was a dense qua
 - 🧪 We have promoted 7 components from the lab to the core: Alert, Autocomplete, Pagination, Rating, Skeleton, SpeedDial, and ToggleButton.
   Thank you for all your feedback on these components.
   While we still plan a couple of breaking changes on them, we are confident that they have reached the same level of quality as the other core components.
-- 👮 We have introduced a new component in the lab, the [TrapFocus](https://mui.com/components/trap-focus/). It manages focus for its descendants. This is useful when implementing overlays such as modal dialogs, which should not allow the focus to escape while open:
+- 👮 We have introduced a new component in the lab, the [TrapFocus](https://mui.com/base/react-trap-focus/). It manages focus for its descendants. This is useful when implementing overlays such as modal dialogs, which should not allow the focus to escape while open:
 
   <video autoplay muted loop style="max-height: 416px; margin-bottom: 24px;">
     <source src="/static/blog/2020-q3-update/trap-focus.mp4" type="video/mp4" />

docs/pages/blog/2021-q1-update.md

@@ -44,7 +44,7 @@ Here are the most significant improvements since December 2020.
 
   <img src="/static/blog/2021-q1-update/stack.png" alt="" style="width: 502px; margin-bottom: 16px;" />
 
-  You can find [more details](https://mui.com/components/stack/) in the documentation.
+  You can find [more details](https://mui.com/material-ui/react-stack/) in the documentation.
 
 - 🎨 We have improved the support for custom colors and variants.
   This is [one](https://github.com/mui/material-ui/issues/13875) of the most upvoted issues in the GitHub issue tracker.

docs/pages/blog/2021-q2-update.md

@@ -43,31 +43,31 @@ Here are the most significant improvements since March 2021.
 - ⚒️ We added a [codemod CLI](https://github.com/mui/material-ui/tree/HEAD/packages/mui-codemod) and 17 transformations (so far) to automatically migrate codebases from v4 to v5.
   If you're not familiar with what a codemod is, check out [Effective Refactoring with Codemods by Edd Yerburgh](https://www.youtube.com/watch?v=H9qtLutnT_g).
 
-- 💄 We have [updated the style of the Slider](https://mui.com/components/slider/#sizes) to better match the Material Design guidelines, and kept a similar style as before under `size="small"`:
+- 💄 We have [updated the style of the Slider](https://mui.com/material-ui/react-slider/#sizes) to better match the Material Design guidelines, and kept a similar style as before under `size="small"`:
 
-  <a href="https://mui.com/components/slider/#sizes"><img loading="lazy" src="/static/blog/2021-q2-update/slider.png" alt="" style="width: 838px; margin-bottom: 16px;" /></a>
+  <a href="https://mui.com/material-ui/react-slider/#sizes"><img loading="lazy" src="/static/blog/2021-q2-update/slider.png" alt="" style="width: 838px; margin-bottom: 16px;" /></a>
 
 - ✨ The new style engine has unlocked problems on the `Grid` component that we couldn't solve before with JSS:
 
-  We have added support for [row & column](https://mui.com/components/grid/#row-amp-column-spacing) spacing:
+  We have added support for [row & column](https://mui.com/material-ui/react-grid/#row-amp-column-spacing) spacing:
 
 ```jsx
 <Grid container rowSpacing={1} columnSpacing={2} />
 ```
 
-We have added support for [responsive values](https://mui.com/components/grid/#responsive-values) on all the props:
+We have added support for [responsive values](https://mui.com/material-ui/react-grid/#responsive-values) on all the props:
 
 ```jsx
 <Grid container spacing={{ xs: 2, md: 3 }} />
 ```
 
-We have added support for a different [number of columns](https://mui.com/components/grid/#columns) than 12:
+We have added support for a different [number of columns](https://mui.com/material-ui/react-grid/#columns) than 12:
 
 ```jsx
 <Grid container columns={16}>
 ```
 
-We have added an alternative implementation that uses [CSS grid](https://mui.com/components/grid/#css-grid-layout):
+We have added an alternative implementation that uses [CSS grid](https://mui.com/material-ui/react-grid/#css-grid-layout):
 
 ```jsx
 <Box display="grid" gridTemplateColumns="repeat(12, 1fr)" gap={2}>
@@ -88,7 +88,7 @@ We have added an alternative implementation that uses [CSS grid](https://mui.com
 
 - 💄 We have improved the accessibility of the Link component:
 
-  <a href="https://mui.com/components/links/">
+  <a href="https://mui.com/material-ui/react-link/">
     <img loading="lazy" src="/static/blog/2021-q2-update/link.png" alt="" style="width: 129px; margin-bottom: 16px;" />
   </a>
 
@@ -216,7 +216,7 @@ We have the following objectives:
   We want to make the upgrade feel painless.
 - ⚛️ Support [React 18](https://reactjs.org/blog/2021/06/08/the-plan-for-react-18.html). [Sebastian](https://github.com/eps1lon) is part of the React [Working Group](https://github.com/reactwg/react-18/discussions), focusing on making us ready ahead of time.
   We want our most demanding users to feel empowered by MUI, not slowed down by a third-party.
-- 🦴 Migrate more components to `@mui/base`. [Michał](https://github.com/michaldudak) has recently added support for the [Switch](https://mui.com/components/switches/#unstyled).
+- 🦴 Migrate more components to `@mui/base`. [Michał](https://github.com/michaldudak) has recently added support for the [Switch](https://mui.com/base/react-switch/).
   You can follow our progress in the [umbrella issue](https://github.com/mui/material-ui/issues/27170).
 - 🌈 Do a proof of concept on supporting a second design system.
   Some of our users (and potential users) dislike Material Design. We will try to make the second design system one that they love!

docs/pages/blog/2021-q3-update.md

@@ -194,7 +194,7 @@ We'll do our best, no guarantee!
   In the last few weeks, we have seen a strong influx of feedback from the community.
   We need to make the most of this feedback to solve regressions, improve the documentation for the new APIs, adjust the tradeoffs we took in the light of more information, and more.
   [15%](https://npm-stat.com/charts.html?package=%40material-ui%2Fcore&package=%40mui%2Fmaterial&from=2020-10-25&to=2021-10-15) of the community has migrated, so far.
-- 🦴 Migrate more components to `@mui/base`. [Michał](https://github.com/michaldudak) has recently added support for the [Button](https://mui.com/components/buttons/#unstyled).
+- 🦴 Migrate more components to `@mui/base`. [Michał](https://github.com/michaldudak) has recently added support for the [Button](https://mui.com/base/react-button/).
   You can follow our progress in the [umbrella issue](https://github.com/mui/material-ui/issues/27170).
 - 🎨 We are [exploring](https://github.com/mui/material-ui/discussions/29024) the introduction of CSS variables.
   Since v5, MUI is no longer actively supporting IE 11. Dropping this browser requirement unlocks new capabilities of the web platform.

docs/pages/blog/benny-joo-joining.md

@@ -11,7 +11,7 @@ He has started last month full-time and is now part of the Core team.
 
 Before joining full-time, Benny was our first intern during the summer.
 He joined us right after graduating from The University of Edinburgh.
-He had a great start with his internship, implementing the [Masonry component](https://mui.com/components/masonry/)! It was one of the [most upvoted issues](https://github.com/mui/material-ui/issues/17000) that we simply didn't have the bandwidth to work on.
+He had a great start with his internship, implementing the [Masonry component](https://mui.com/material-ui/react-masonry/)! It was one of the [most upvoted issues](https://github.com/mui/material-ui/issues/17000) that we simply didn't have the bandwidth to work on.
 
 As part of the Core team, he will help with the community support, as well as work on some of the new features we plan for the community version of the library, like the unstyled components and the second design system.
 I am excited to see what other valuable contributions he will make in the future.

docs/pages/blog/december-2019-update.md

@@ -8,7 +8,7 @@ tags: ['Company']
 
 Here are the most significant improvements in December:
 
-- 🚨 We have introduced a new [Alert](https://mui.com/components/alert/) component in the lab, thanks to **[@dimitropoulos](https://github.com/dimitropoulos)** ([#18702](https://github.com/mui/material-ui/pull/18702)). The component also supports composition with a [Snackbar](/material-ui/react-snackbar/#customized-snackbars).
+- 🚨 We have introduced a new [Alert](https://v4.mui.com/components/alert/) component in the lab, thanks to **[@dimitropoulos](https://github.com/dimitropoulos)** ([#18702](https://github.com/mui/material-ui/pull/18702)). The component also supports composition with a [Snackbar](https://v4.mui.com/components/snackbars/#customized-snackbars).
 
   ![Alert](/static/blog/december-2019-update/alert.png)
 
@@ -18,15 +18,15 @@ Here are the most significant improvements in December:
 
   <p class="blog-description">Filled variant</p>
 
-- 👤 We have added [stacking](/material-ui/react-avatar/#grouped) support to the avatar.
+- 👤 We have added [stacking](https://v4.mui.com/components/avatars/#grouped) support to the avatar.
 
   ![Stacking](/static/blog/december-2019-update/stacking.png)
 
-- ↕️ We have added [vertical](/material-ui/react-button/#group-orientation) support to the button group.
+- ↕️ We have added [vertical](https://v4.mui.com/components/button-group/#vertical-group) support to the button group.
 
   ![Vertical button](/static/blog/december-2019-update/vertical-buttons.png)
 
-- 🌎 We have almost doubled the number of supported [locales](/material-ui/guides/localization/#localization) from 13 to 22, thanks to our awesome contributors. [Help us](https://github.com/mui/material-ui/blob/next/packages/material-ui/src/locale/index.js) double this number next month 🚀!
+- 🌎 We have almost doubled the number of supported [locales](https://v4.mui.com/guides/localization/#supported-locales) from 13 to 22, thanks to our awesome contributors. Help us double this number next month 🚀!
 
 But this summary is just scratching the surface. We have accepted 168 commits from 73 different contributors. We have changed 1,059 files with 13,468 additions and 8,584 deletions.
 

docs/pages/blog/spotlight-damien-tassone.md

@@ -11,7 +11,7 @@ A few months ago, right in the middle of the COVID-19 outbreak, [Damien Tassone]
 
 Prior to joining MUI, Damien worked in the finance industry in London for a decade. Part of the initial Agile Market team at RBS, and more recently leading a large Commodity Trading application at Adaptive, Damien has developed his React experience as part of large projects where Components driven design plays a huge role in successfully delivering applications. He loves TypeScript.
 
-Right from the start, Damien has made fast and significant progress. He has been an amazing addition to the team, and thanks to him, we are on the verge of releasing a new advanced component: the [Data Grid](https://mui.com/components/data-grid).
+Right from the start, Damien has made fast and significant progress. He has been an amazing addition to the team, and thanks to him, we are on the verge of releasing a new advanced component: the [Data Grid](https://v4.mui.com/components/data-grid).
 
 <img src="/static/blog/spotlight-damien-tassone/data-grid.png" style="margin-bottom: 3rem;" alt="Data Grid" />
 

docs/src/modules/components/AppNavDrawer.js

@@ -393,7 +393,7 @@ function reduceChildRoutes(context) {
       : false;
     let firstChild = page.children[0];
 
-    if (firstChild.subheader && firstChild.subheader.children) {
+    if (firstChild.subheader && firstChild.children) {
       firstChild = firstChild.children[0];
     }