Moving Mouse Locks Screen - potential fix
There are a few outstanding questions about this and I had the same problem.
2022 moving mouse locks screen - Apple Community
2019 moving mouse locks screen - Apple Community
Turned out to be the Hot Corners shortcut that was doing it for me - for some reason at some point it had assigned the screensaver to the bottom left corner. Reset it to "-" and all good:
https://macpaw.com/how-to/lock-mac-screen
3. Set up a hot corner
Hot corners allow you to drag the mouse pointer to one of the four
corners of the screen to initiate an action – you can use one as a sleep
shortcut on your Mac. To set it up:
- Launch System Preferences.
- Choose the Desktop & Screen Saver pane.
- Click the Hot Corners button at the bottom right of the window.
- In the drop-down window, choose a corner.
- Click on the menu and choose either Start Screen Saver or Put Display to Sleep.
MacBook Pro 15″, macOS 12.3