As the title suggests, I’ve been dealing with this issue since I started using Linux as my main operating system.
The only way I can achieve 240 Hz at 4K resolution in Linux on my Samsung G80SD monitor is by using a DP 1.4 cable, which introduces artifact flickering when selecting either 120 Hz or 240 Hz as mentioned in this thread. This happens to me on both Linux and Windows.
With the HDMI 2.1 cable however, the connection is perfectly stable and solid up to the entire 240 Hz in Windows 11, but only up to 120 Hz in Linux. When I select 240 Hz in KDE’s display settings panel, the entire system behaves very sluggish, as if it were running at exactly 60 Hz just as I confirmed using the Blur Busters’ TestUFO (even though everything indicates that internally it’s running at 240 Hz timings, including the monitor’s OSD and even KDE Plasma’s FPS display tool).
Is this a limitation of the HDMI 2.1 protocol on Linux? I understand there were issues with AMD, but I’m not sure what the current state is with Nvidia.
System info:
Distro: NixOS unstable channel
Kernel: 6.15
Nvidia driver: 575.57.08
DE: KDE Plasma 6.3.5
Monitor: Samsung Odyssey G80SD