Short summary:
Maybe a fair phone? https://shop.fairphone.com/fairphone-5
Works like this for me:
Tap password field
Bitwarden pops up requesting fingerprint to unlock
Select the credentials you want to use
Autofill
Not quite sure what you mean by fully unlocked here. I don’t see the problem with all credentials being unlocked if you have to unlock on every access to the db.
Your profile pic put your comment in the right light.