I think in my previous post, I answered most of it… here an addition: “Favorites” never had the auto-fill behaviour per se. Here: New extension: New (and only) "Vault" tab - Pros, Cons, Differences, Improvements?! right in the first post you can see, that in the old extension, the “Favorites” were in the “Vault” tab and by clicking them you got into “item view”.
So, favorites per se having “auto-fill functionality” would not be the “old behaviour”. - For cards and identities, there was autofill functionality before - and that maybe should indeed be restored (see the feature request in my previous post).
With passwords (login items) it should work. Autofill suggestions contain login items. Or can’t you auto-fill login items now?