The image area flashes continuously - just getting brighter and darker endlessly.
Thanks for the response, David. My card driver is kept up to date by MacOS, which is up to date. Regarding the GPU processing, it just seems that I should be able to use the hardware I paid for with the software I paid for. But I did go in to check those settings, and they were set to Basic. I put them on normal, then went back to that same file in Photoshop, but I can no longer reproduce this flashing, not with the Normal setting nor the Basic one. Hate when that happens - intermittent errors. When it happens again, and I'm sure it will, I'll try adjusting those settings again.