PS Version 27.8 does not work with iMac (Intel with AMD)

What model and year is your iMac?

The first thing I would suggest trying is holding down Shift while starting Photoshop to skip loading any third party or optional plugins and see Photoshop starts.

I would try it even if you don’t have any third party or optional plugins that you are aware of installed.

If you upgraded from an earlier version of Photoshop 2026, it may also be worth trying a reset of the Photoshop preferences:

https://helpx.adobe.com/photoshop/desktop/get-started/settings-and-preferences/reset-preferences.html

If nether of the above do any good, perhaps posting the contents of Help>System Info from within Photoshop will give us some clues as to why 27.8 is not working on your iMac.

I have a 2019 Mac Pro. OS Tahoe 26.5.2. 3.3GHz, 12 core Intel Xeon W. AMD Radeon Pro Vega II 32GB. 96 GB memory. Just checked. A bit more power but definitely old in computer years. I’m running photoshop 27.8.0 ok. So far it’s acting a bit better than the last release. I had major trouble with the last release not opening pdfs. Had to mess around with support. Frustrating because support via CC chat was seriously uneven. Finally I called on the phone and got a person who knew something about it. In the end I had to uninstall, reinstall, and rebuild my workspace. As well as turn off Mac, turn on again. So far, since then, it’s worked, except for beachballs using the smudge tool - which seems to have a major glitch now. Photoshop is also slower than it used to be.