Hi there i have had an Nvidia 3080 and switched over to the 6800XT.
With Nvidia i have had a similar Problem. Nvidia fixed it with a Driver Update so i hope AMD will with this, too.
The Problem itself is:
It doesn't work with my Samsung Odyssey G9 Monitor at 240 Hz, right now the maximum is 120Hz.
The screen gets massive coruption when I try to set the refresh rate to 240Hz, what was working well before (Nvidia 3080).
Monitor is the latest Firmware 1008.1
Model: LG49G94TSSUXZG
Driver Version: Adrenalin 2020 Edition 20.11.3 Optional
and i am using a official AMD 6800XT.
So hopefully AMD will fix this soon.