I’ve searched a bit about reverse prime, and there’s an entry about it on arch wiki, however it seems it’s only about X11 configuration and nothing about Wayland or anything else.
Well, at least with my current setup I can get VRR working on my main display without needing to disable my secondary one with my NVIDIA card.
Probably not, as the image says Zen is based on the latest Firefox and Floorp isn’t.