I'm using two monitors, with the primary display capable of 240 Hz and the second limited to 60 Hz. When both monitors are connected over HDMI, they work, but selecting 240 Hz on the main display causes its brightness to become extremely low and the brightness controls stop working. The main monitor works normally at 240 Hz when the second display is disconnected, and both displays also look fine when they are set to 60 Hz. I've reproduced the problem across several Linux distributions, including systems using Wayland, while the monitors work correctly in Windows. Is there a way to use the monitors at 240 Hz and 60 Hz simultaneously without the brightness issue?
2 Answers
This behavior may depend on the specific distribution, compositor, or driver combination. It has been reported on some gaming-focused Linux setups while working normally on others, so testing a different Wayland compositor or updating the graphics stack could help narrow it down. Also check whether the 240 Hz display is using the correct HDMI mode, cable, color format, and full-range output settings.
This can happen with older display servers because they may not handle independent refresh rates properly across multiple monitors. A modern Wayland session, such as those provided by GNOME or KDE Plasma, is generally the better option. However, since you’ve already seen the problem on Wayland systems, the issue may instead be related to the graphics driver, HDMI link configuration, or how the monitor handles high-refresh-rate output.
I tested this on Fedora and CachyOS, and both appeared to be using Wayland, but the brightness problem still occurred.