Today my screenshot isn't working and it normally has no issues... How can I troubleshoot this?

Start with this...

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes.

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.

Starting today, Dec 28, when I take a screenshot on either my iMac or Macbook Pro, (both running Monterey 12.1) using shift-command-4, the screen shot gets taken, but after I select "save to photos", the image remains on the screen, even after clicking "done". A sound is made, when clicking, but the image stays frozen on the screen and the only way to remove it is by restarting the mac.

I ran a malware scan and it looks good, i reset the VRAM as someone suggested, and I booted up in safe mode. Nothing works.

I noticed that the screenshot.app file did not exist on my imac until Dec 7, 2021. I also that there a number of files in UTLITIES that were added on Dec 7th. Ironic about the date. Could this be a virus? I'm truly baffled, any help will be appreciated.

I've been having that exact same issue. I opened Utilities and found that the Screenshot app along with most of the other files had been last modified December 7th too, my guess would be because of an update?

For an unrelated reason I recently completely erased and reinstalled macOS Monterey 12.1 and that's when I first noticed the issue.

It's really annoying because I use Command + Shift + 4 all the time, although I've noticed that if I force quit (Command + Q) when the issue is happening it normally resolves without needing a restart. My guess is the Screenshot app must be running in the background, although I'm not sure why is has been freezing up.

I have the exact same problem. I also noticed that the screenshot utility has been updated on Dec 7th 2021. The only way out is now to reboot the laptop