I’m sorry you’re dealing with that, especially given what’s stored in those notes.
If you protected the notes with a custom Notes password and have forgotten it, resetting that password will not unlock notes that were already locked with the old password. Apple is explicit about that.
Before changing anything, I’d try opening one of the locked notes and see whether Face ID is offered. If Face ID had previously been enabled for Notes and still works, you may be able to open the note and immediately copy the contents somewhere safe.
I would not reset the Notes password yet, because that won’t recover access to the existing locked notes and could make things more confusing.
If Face ID isn’t available, do you have another Apple device where you previously opened these same locked notes, such as an iPad or Mac?
A friendly note: This is the German-language Apple Support Community. Posting your question in German will make it easier for more members to understand it and offer assistance.