[5.x]: Custom Date Fields not respecting site timezone in CSV exports

[watarutmnh]

What happened?

Description

When exporting entries to CSV, custom Date fields are exported in UTC format, while system fields (dateCreated, dateUpdated) are correctly exported in the site's configured timezone (JST/UTC+9).

Steps to reproduce

1. Configure Craft CMS site timezone to 'Asia/Tokyo' in config/general.php
2. Create a custom Date field (with "Show Time Field" disabled)
3. Create an entry and set a date value
4. Export entries to CSV using the Expanded format

Expected behavior

Custom Date fields should be exported in the site's configured timezone (JST/UTC+9), matching the behavior of system fields.

Actual behavior

• System fields (dateCreated, dateUpdated): Correctly exported in JST (UTC+9)
  Example: 2025-01-22T15:08:50+09:00
• Custom Date fields: Exported in UTC
  Example: {"date":"1974-03-16 15:00:00"}

Additional Notes

• This issue was observed after updating to 5.6.1, which fixed timezone handling for system fields in CSV exports (PR expanded export and datetime attrributes #16447)
• The Control Panel correctly displays all dates in JST
• Database correctly stores dates in UTC

Craft CMS version

Craft CMS version: 5.6.1

PHP version

PHP version: 8.4

Operating system and version

No response

Database type and version

Database: MySQL 8.0.40

Image driver and version

No response

Installed plugins and versions

[i-just]

Hi, thanks for reporting! I raised a PR for this. It targets 4.15 and 5.7, as that’s a slight change in behaviour.