Error in the admin: editor.css not being applied

[strarsis]

How to use compiled css within add_editor_style();

Adding editor styles should be the same for Classic Editor as for the Gutenberg editor. For Gutenberg editor this approach is used, with a relative path, as this works correctly with style post-processing:

You may also find this example interesting (Sage 10 FSE sample theme):
https://github.com/strarsis/sage10-fse/blob/e7bc7db0bd8b4b8876aca7b521d8c4b970c9b876/app/setup.php#L38-L39