Clokwork Which macbook did you use with it? (or pc). Which color profile did you use with zenscreen? Have you applied differing off terminal commands ? Have you tried betterDisplay app also? - The reason I'm asking, since you need to tackle the beast one by one. I would really want to find out whether zenscreen emilinates PWM flicker cause, and the rest could be handled by all these workarounds, including tunring off font-smoothing.
Then if it all works, you go go headless with macbook air m1 for example, snapping off crappy screen.