Face recognition speeds entry of your Note password, it doesn’t replace it. (much the same way it eases routine entry of your passcode when unlocking your device)
For notes currently locked where FaceID doesn’t work, you MUST enter the password; there is no other workaround and no “backdoor” or reset mechanism.
Notes are already secured by multiple layers of cryptologically secure - but recoverable - means.
Adding an additional password is an optional, “extra security layer” for which the user takes full responsibility for recovery.
See following iOS User Guide excerpt:
“ … Important: If you forget your notes password, and you can’t use Face ID or Touch ID to unlock your notes, you won’t be able to view your locked notes, and Apple can’t help you regain access to those locked notes …”
More detail on using FaceID going forward is at following reference.
Ref: https://support.apple.com/en-au/guide/iphone/iphf177bb154/ios