Rtx 3090 linux samsung g9 no 240Hz support

Problem: I dont have an option to sselect 240Hz refresh rate (limits to 120Hz) on widescreen monitor for 5120x1440 res using latest nvidia drivers on any linux distribution .
In windows 10 all works fine - same machine. Problem is in nvidia drivers
I tried to use xrandr and add custom modes but it doesnt work. Can you please help?
p.s. Samsung g9 5120x1440@240Hz - doesn't work (nvidia rtx3090) - Graphics & Display - Manjaro Linux Forum on this forum are results of my xrandr and attempts to add custom res. (not to pollute this post)

Might be related to this:
https://forums.developer.nvidia.com/t/8k60-output-with-rtx-3070-and-samsung-q900ts-over-hdmi-2-1/167227
Please create a xorg.conf with
Option “ModeDebug” “true”
in device section set, reboot and run nvidia-bug-report.sh as root and attach the resulting nvidia-bug-report.log.gz file to your post.