Hello,
Apple has several documents helping you with Face ID.
This Support article is specific to seeing a 'disabled' Face ID alert, and explains what to do when you see that notice or an issue with the TrueDepth camera. --> If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support
Unless a software update solves the problem you may need to have Apple take a look at your device. Use this link to set up an appointment —> Genius Bar Reservation and Apple Support Options - Apple and this one to get a repair estimate —> iPhone Repair & Service - Apple Support
If you don't see a 'disabled' message but do have general issues with Face ID not working properly, explore the list of things to try in this document: If Face ID isn't working on your iPhone or iPad Pro - Apple Support
If the first 8 don't solve the issue then use #9, contact Apple.
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Click on this link to read how to lock notes on your iPhone, iPad, and iPod touch --> How to lock or unlock notes on your iPhone or iPad - Apple Support
"Beginning in iOS 16, you have two options to lock your notes. You can lock notes with your iPhone passcode. Or, you can create a unique password only for Notes.
If you use your iPhone passcode, you don't have to create and remember a separate password. If you access your iCloud notes on more than one Apple device, use the passcode or login password for that device to unlock those notes.
If you use a unique password for Notes, there is no way to access your locked notes if you forget the password. If you forget this password, you can reset your notes password and use your new password to lock other notes. If you access your iCloud notes on more than one Apple device, use the same notes password to lock and unlock all of them."
Read the support article for details.