I use Ubuntu 24.04 with a 4k monitor. On X11, I set 60 Hz and I get 60 FPS when testing using the UFO Test website.
When I try Wayland, the settings say it's set at 60 Hz as welll, but it's no way 60 Hz, and when I test it using UFO Test, it shows only 30 FPS.
I have nvidia-driver-550. I tested the PPA with nvidia-driver-560 driver, but I still have the same issue.
What could be the reason?
I suppose that you use a laptop and you connect your monitor through HDMI. If that's indeed the case, then the problem is that NVIDIA doesn't yet support Wayland (or the other way around) 100%. So using Wayland with NVIDIA cards presents laggy behavior and lower FPS than what you set in the Display settings.
I also have the same issue and haven't yet found a solution (because there isn't another one) other than using Xorg instead of Wayland. The issue will be likely solved when NVIDIA decides to improve their Linux driver and fully support Wayland. Until then, Xorg is your (our) friend.
Below are some relevant posts I have found about the matter, none containing a solution but indicating that there is none yet, unfortunately: