screen saver runs in background and will not shut off OS12.6 iMac

Hi R.D.C,

Thanks for using Apple Support Communities. It sounds like you're seeing an alert that your Mac restarted because of a problem. If that's the case, use these steps to help resolve that:

If your Mac restarted because of a problem - Apple Support

"Check your software

If the issue is caused by software on your Mac, one of these steps might help:

• Install all available software updates.
• If your Mac suspects that a particular app caused the restart, it might ask whether you would like to move the app to the Trash. Click Move to Trash, then contact the software developer to see if a software update is available.
• Use safe mode to try to isolate the cause of the issue.
• Reinstall macOS. If the issue continues after reinstalling macOS, check your hardware.

Check your hardware

Learn how to check your connected devices and other hardware.

Check peripheral devices first

If you don't have any devices attached to your Mac, skip to the next section.

1. Shut down your Mac.
2. Disconnect all peripheral devices, such as hard drives or printers. If you have a desktop Mac, make sure that only a display, keyboard, and mouse or trackpad are connected.
3. Turn on your Mac.
4. Use your Mac for the amount of time that it would usually take for an unexpected restart to occur.
5. If an unexpected restart occurs, follow the steps to check the internal RAM and third-party hardware.
6. If an unexpected restart doesn't occur, turn off the Mac and connect one peripheral device at a time until an unexpected restart occurs."

You mentioned a screen saver that is running, can you tell us more about where you're seeing that run in the background?

Thanks.

We appreciate you keeping us updated!

We're glad to hear that it's working for you again. If the behavior reappears, let us know if those steps help.

That being said, if you have questions or concerns in the future, please don't hesitate to reach out to us here on Apple Support Communities.

Have a lovely weekend!