UPDATE / SOLUTION:
Got it working!
The Photoshop 2021 application is a ”Universal” app, compiled to run on either M1 (Apple Silicon) or Intel architecture - and, of course, it prefers to run on Apple Silicon if it’s on an M1 machine.
If you look at the ”Get Info” panel for the Photoshop app, there’s a checkbox to ”Open using Rosetta”. That converts the Intel-compiled code to run on M1 and all the usual stuff just works.
The problem is that Autodesk has not updated the ShotGrid extension to run on native Apple Silicon. In any case, that’s the fix - simple, once you know it. (“It’s always a checkbox.”)
The docs are on this page: https://helpx.adobe.com/photoshop/kb/photoshop-for-apple-silicon.html in the ”M1 native known issues“ section - Issue ”Missing or unsupported extensions“.
This Apple Support page shows where to enable the checkbox in the ”Which of your apps need Rosetta?” section: https://support.apple.com/en-us/HT211861
Also, this from Autodesk Support:
“I was able to confirm with our Development Team that this is a known issue. They are working on the compatibility with the M1.”