there's the lockdown or similar feature at the phone level in Android and iOS
if you're in a situation where you don't want someone to access Bitwarden, then you probably also want to stop them from using your browser with all the cookies and logins it currently has
so temporarily block all biometric access on your phone in such cases, and merrily enjoy biometric access when you're physically safe again
on Android, it's Power + Volume-Up, then Lockdown