Steps to reproduce the issue

I was reading through the code (!) and came upon this line in
layouts/plugins/webauthn/manage.php (lines 43-44)

$app->getDocument()->getWebAssetManager()
        ->registerAndUseStyle('plg_system_webauthn.backend', 'plg_system_webauthn/backend.css');

Expected result

File backend.css is loaded.

Actual result

There is no backend.css anywhere. The file does not seem to exist.
Was button.css meant to be loaded instead?

System information (as much as possible)

Since Joomla 4.0 !?

Additional comments