.ims files? Screen shots disappear?

This is bizarre...

Using  Mac PS Elements 2020 18.0 on Catalina 10/15.7...  

In the past 3 days, a few dozen .jpegs that began as Screen Shots have all been transformed magically into .ims files and will not open in PSE ...nor will they reconvert by simplying overwritign the format back to jpg or jpeg. WTF?

What's more, many older screen shots and renamed screen shot images that were JPEGs  have just ... disappeared completely. Of my main, external, and backup drives.

I have not upgraded/updated teh MAc OS, and I do not believe any Adobe PSE updates slipped through. I think. But what would DO this?