A new version of Photoshop to download today. Not too busy so installed it to try out. Some useful speed improvements noted on painting masks etc but then came up against flickering images redraws and missing segments of images.
It would appear that Adobe are updating the drawing code to work better with multi core video cards. This is a pretty nice development but it looks to be an early version and Adobe themselves indicate that images may not display correctly.
Whilst they work it out I have gone into preferences (cmd or control K) and selected the Technology Previews tab and ticked the box named “Deactivate Native Canvas”. This fixed the redraw problem for me.
Im using a pretty serious mainstream graphics card (An RTX 3080Ti) so hopefully they will sort this quickly and so allow me to use the card more efficiently in future.
UPDATE: the earlier fix of unticking “Multithreaded compositing” in the Performance tab of Preferences also works but this new method fixes the problem and you can leave Multithreaded compositing ticked for extra performance.