If you find that you can no longer close the screensaver in Windows 10 by moving your mouse or pressing a key on the keyboard, we have found the most common cause of this is a setting in the screensaver.
To fix this, follow these steps:
Search for Screen saver in the Windows 10 search bar and select Change screen saver.
Otherwise you can go Settings > Personalisation > Lock Screen and scroll down to the very bottom and click on Screen saver settings
Under the Screen saver tab change Windows Gallery to Photos