Had a tester with one of the new MacBook Pros find an app just black-screened with MSAA 8x, but was fine if 4x.
I have since seen various mentions of no 8x support on M1s but not seen anything concrete specs-wise.
Regardless Unity should limit the MSAA level usable if this is the case and it doesn’t currently (at least not in Unity 2020 LTS, HDRP).