Steps to reproduce the issue

1. Use media type field with subfields
2. Go to articles and click on +
3. You can't use the media button until article saved, and then it can function properly. (So if I want 4 repeatable fields, I create 4 empty fields and save to use.

Expected result

When using subforms, when you click on add button, expected to be able to directly use the media button to input image.

Actual result

You won't be able to use the media button in subfields until article is saved.

System information (as much as possible)

Joomla! 4.0.0-beta7
PHP 7.3.27
mysql 5.6.41-84.1

Additional comments

This is my first time posting an issue, so let me know if I should improve on anything! Thanks!