The issue with the bystanders is described in this thread linked below. I don’t know if it’s related to the flickering screen issue - my guess is probably not but I don’t think Zwift have responded to the bug in which bystanders change to the color of a nearby pace partner or holo replay. On my M1 mac I always see the strangely colored bystanders but have never seen the other weird color flashes taking over the display, even in large groups in Neokyo where it seems to be common.