You got a bit more lucky than the last person trying to get the 16" MBP 2019 working. On Catalina it failed completely. See here:
Apparently they fixed Big Sur at least to the point where you can make it to an onscreen window and then sync failure – so the machine is not utterly useless for all tasks and could run at least trivial tasks.
This machine uses the new AMD Navi graphics chips with DCN display engines. These are not supported at all by our PsychtoolboxKernelDriver, and most likely never will be, which means that all high precision visual timing and most of PTB’s diagnostics and workarounds for operating system bugs are dead. This makes the machine very untrustworthy for precise timing. You are essentially on your own here.
So you don’t need to bother with the PsychtoolboxKernelDriver, it won’t help.
Seems we can rule out Retina display trouble as well, given you seem to run on an external display with 1920x1080@60Hz here.
What you observe could be really bad operating system timing, or more likely desktop compositor interference, no way to distinguish without use of external timing measurement equipment like photodiodes, VPixx devices or similar
As the text says already, if this happens on repeated runs, you can add Screen(‘Preference’, ‘SkipSyncTests’, 2); to disable sync tests and use the machine for tasks which do not require any trustworthy or accurate timing at all.
Or if this is a machine mostly used for serious data collection you could sell the machine and replace it by a much more suitable Linux laptop for less than half of the purchase price.
You could also consider trying all the things mentioned in this discussion thread, to contribute some data-point that may help fixing your machine sometime in the future. You can skip everything related to the PsychtoolboxKernelDriver ofc.: