I'm having the same issue as posted here: https://www.reddit.com/r/pico8/comments/g45cpk/interface_shimmer_on_macos/
Pico-8 ver 0.2.5c
"Is anybody experiencing this? It was blinking for a while, restart did not help, then I got distracted with something and now it's okay again.
Update: Then it shimmers again. It is just random. And it’s very annoying, as there is no way to fix it.