Hey there Tobi2023,
The first thing we wanted to provide was the article that includes the steps to change your Mac user account password: If you forgot your Mac login password
If those are the steps you're following, and you've already scrolled down the terms/conditions screen, then we'd like to help by learning more about what's occurring. We also want to rule out some basics:
- What exactly occurs when you try logging into your user account as you were able to do this without any issues a few days ago? The more details you provide, the better we'll understand what's happening.
- Did you notice this occurring after installing a new app, changing a setting, etc.?
- Sometimes unexpected behavior can be resolved with a restart. Check out the section ‘Restart your Mac' here: Shut down or restart your Mac
Cheers!