I’ve been playing around with it today. I first noticed the issue when I migrated to the M2, turned off the graphics processor and it went away - forgot about the issue.
However, I had noticed something when I started up both the M2 and now the M4 that I wondered about - I get a quick notification on the screen as the computer is starting up that says something about increasing contrast.
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I have no idea where that came from, it appears and then disappears quickly. It does NOT appear when I switch to the second user. I first noticed it when I was setting up the M2Max computer and while I found the additional contrast annoying, it wasn’t enough to bother me. At the time I had an X-Rite i1Pro calibrator and it’s i1Profiler software. At the time the calibrator didn’t work on the M2Max computers and I never tried to use it later on - I ended up buying the Calibrite.
This morning I deleted all the i1Profiler stuff (since I don’t need it), but it didn’t make a difference.