Selection display problem

[douge85378629]

I just upgrade from Photoshop Elements 13 to PSE 2021. So far so good. Except...

When I use the Rectangular Marquee Tool, the selected area is filled with a randomly-shaded area that pulses on and off each second. (Example attached over a blank graphic.) It's very annoying. Is this a feature that I am able to turn off? ...Doug