Image editor not working in child theme

Can you edit the image using WordPress’s built-in tools with FileBird deactivated?

Thank you for answering. It has nothing to do with FileBird.

I removed whitespace at the end of functions.php! The image preview in the child theme now works correctly. As a .NET C# programmer, what strange programming universe have I entered into? Whitespace breaks a feature?

The fix is described here:

https://wordpress.stackexchange.com/questions/292723/edit-image-preview-is-not-displayed

what strange programming universe have I entered into? Whitespace breaks a feature?

You have entered the wonderful world of PHP. 😉