Hey bazzap1966,
It sounds like there's an issue with the Notes app itself as you're not able to create new notes either. Let's get the Notes app working as expected, then work through restoring the lost notes from your Time Machine backup. Let's start with isolating this and narrowing our focus by using safe mode and a test user account.
Safe mode will help to rule out software as a possible cause. Here's more information on safe mode and how to start there: How to use safe mode on your Mac - Apple Support
There are steps included in that guide for if the issue does or doesn't continue while started to safe mode. Be sure to follow the appropriate steps, and check to see if you can create a new note while started to safe mode.
If the issue doesn't resolve with the steps from that guide, create a new user account to see if the behavior happens there too. This will let us know if the issue is system-wide or only within your user account: Set up users, guests, and groups on Mac - Apple Support
Let us know the results. Also, which macOS version is installed as menu options can vary by version. To find out select the Apple menu > About This Mac > Overview.
Take care!
