I have this exact same issue with the same G80SD monitor, and like you, I use NixOS (but with KDE Plasma as the desktop environment). I went crazy even trying to report it as a KDE bug, but it’s clearly an issue related to the HDMI 2.1 protocol on Linux and Nvidia.
A couple of notes that might be useful for @abchauhan:
- Stability with HDMI 2.1 at 120 Hz is perfect, with no visible flickering artifacts whatsoever.
- When switching to 240 Hz, the monitor behaves exactly as if 60 Hz were selected (as shown in @starcraft66’s video), and this can also be confirmed using Blur Busters.
- It’s not an issue specific to the desktop environment, as I ran several tests and in all of them the monitor is running at 240 Hz — it’s just that somehow 3/4 of the frames are being dropped or skipped.
- I suspect this might be related to how DSC is implemented in Linux for HDMI 2.1. I know there have been issues with AMD in this regard, but I’m not sure what the current situation is with Nvidia.
- Using a DP 1.4 cable solves the 240 Hz issue — it works correctly and as smooth as butter on my NixOS installation — but it introduces the flickering artifacts mentioned by the OP. Interestingly, these artifacts are also present in Windows 11. I don’t know if this is due to the quality of my DisplayPort cable, the DP port on my monitor, or how DSC works, but the artifacts appear regardless of whether I use Linux or Windows at both 240 Hz and 120 Hz.
This is honestly a very frustrating issue because it prevents us from fully taking advantage of our monitor through HDMI 2.1 when using Linux (even though HDMI is the connection that works best and unlocks the monitor’s full potential in Windows).
As for me, I’m willing to contribute testing and time as needed to help improve HDMI 2.1 support for Nvidia/Linux and find a solution, since it’s quite important for my use case. Even if that means using beta or experimental drivers, I’m open to participating.
Thanks in advance.