As if by magic…
Big Sur offered an OS update today. Ordinarily I wouldn’t download updates until they are fully supported by PTB, but since I’m on a brand new MacBook which is already ‘broken’, I figured there’s nothing to lose by downloading it. And, just like that… keyboard functions are working again in PTB. So, it looks like it was an Apple screwup, but this time around they’ve fixed it themselves.
Not as much luck with stimulus timing or being able to disable the ConserveVRAM workaround, but the point is that with the latest update it’s now possible to run PTB on an M1 for basic debugging.