Which monitor?

Which is better for the xbox series x a 4k 60fps screen or fullhd 144fps?

A 4k monitor delivers better images, but 60hz are only standard. With a 144hz screen, games feel smoother and the response time can improve, especially when playing fast games like e.g. Shooter. If you prefer graphics-intensive games then use the 4k monitor, otherwise the FullHD.

I don't think the games will run on 4 and 120 hz. I would recommend a fhd, 120 hz, ips, 1ms monitor!