I am pretty sure they are synchronized to refresh rate (at least on windows).
I made a small experiment about raf https://codepen.io/mmis1000/pen/qBxqgLr and it always looks uniform regardless I am on a 60, 120, 160 fps screen. (It would blink crazily if you put it in the middle of two screen with different refresh rate, because it can't be in two refresh rate at same time)
Erit: okay, it looks non uniform only in safari. Clap, clap, clap, Apple…