Notes not letting me use Face ID

Unfortunately, what you describe matches the intentional design of the app.

FaceID only serves as a temporary proxy for the underlying password used to originally secure the note.

You are occasionally prompted to use the actual password, and without it you’ll not be able to gain access.

If you forget your custom password, and you can’t use Face ID or Touch ID to access your locked notes, Apple can’t help you regain access to those notes.

See the source of the above summary and the quoted excerpt here:

Lock your notes on iPhone - Apple Support

yahelmtnzz wrote:

So I have a password for all my notes but I tipically use Face ID for them. Today I tried opening a note with my Face ID as usual, but it would only let me use my password. I'm pretty sure I remember (or I don't) but I still can't get it right. I reset my password, turned Face ID off and on again, made a new password and nothing. Face ID works for every new note I make except for the ones that are already made.

Just to add : You create a new password for new notes that you save make sure to write down the a password How to lock or unlock notes on your iPhone or iPad - Apple Support (CA)