Photoshop won't save preferences

I'm on Windows 10 Photoshop version 2021 22.5.9. I haven't updated because my graphics card doesn't support Firefly. However, it's worked great for two years. Yesterday when I quit PS, I got a pop-up saying it couldn't save my preferences because the file was open or in use from another application. I checked permissions and they're all as should be. I'm not sure how to fix this. I do have Carbonite and I keep wondering if the back up somehow flagged the prefs file, so I unmarked it for back up but no luck. I can work but my main entry screen defaults - so none of my recent files show, and my preferences don't load up. Thanks in advance for any help.