https://github.com/laravel/framework/issues/42075

app/Models/Client.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\SoftDeletes;
+
+class Client extends Model
+{
+    use HasFactory;
+    use SoftDeletes;
+}

app/Models/Contract.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\SoftDeletes;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+
+class Contract extends Model
+{
+    use HasFactory;
+    use SoftDeletes;
+
+    public function relationSelf(): HasMany
+    {
+        return $this->hasMany(static::class)->onlyTrashed();
+    }
+
+    public function relationOther(): HasMany
+    {
+        return $this->hasMany(Client::class)->onlyTrashed();
+    }
+}