Many to many relations have the same value in old and attributes

[peirix]

Describe the bug
Basically the same as #1081 but that got closed, so thought I'd create a new one.

We have an Item class that has a many-to-many relationship to Color through the colors():

public function colors()
{
    return $this->belongsToMany(Color::class, 'item_color');
}

And then our getActivitylogOptions is set up as following:

public function getActivitylogOptions(): LogOptions
{
    return LogOptions::defaults()
        ->logFillable()
        ->logOnly(['colors'])
        ->logOnlyDirty();
}

The first thing is that I can't tell it to log ['colors.id'] which I would like to, I then get an error saying id attribute does not exist on collection. But also the old colors array and the attribute colors array are always the same. And I found that if I sync the colors first the arrays will have the new value, and if I save the item before syncing the colors it will have the old value

$item->save(); // in this log the arrays are both the old colors
$item->colors()->sync($request->input('colors'));
$item->save(); //  in this log the arrays are both the new colors

To Reproduce

Schema::create('items', function (Blueprint $table) {
    $table->id();
    $table->string('name')->nullable();
    $table->softDeletes();
    $table->timestamps();
});
Schema::create('colors', function (Blueprint $table) {
    $table->id();
    $table->string('name');
    $table->string('slug');
    $table->string('hex_code');
    $table->timestamps();
});
Schema::create('item_color', function (Blueprint $table) {
    $table->foreignIdFor(Item::class)->constrained('items')->onUpdate('cascade')->onDelete('cascade');
    $table->foreignIdFor(Color::class)->constrained('colors')->onUpdate('cascade')->onDelete('cascade');

    $table->primary(['item_id', 'color_id']);
});

Expected behavior
First off I would expect the arrays to be different, but I would also like to be able to specify what attribute of the related model I would like to be in the array

Versions (please complete the following information)

• PHP: 8.3
• Database: mysql8
• Laravel: 11.19.0
• Package: 4.8.0