Same issue RX6600XT with LG55B9
It's not exclusive to 4K for me, I can't go higher than 60Hz at any resolution when the 'super resolution' is enabled, as in their driver based DLSS competitor, so I never use it. Kind of ironic to be stuck at 60Hz, though it would be useful if they had information about this in the app.
I gave up on the issue due to the amount of time consumed and the lack of results.
You might get lucky with custom resolution utility, but I couldn't get an image back up for a while and jiggled about with extra cables and using iGPU to try and change settings after I lost signal.
free sync is also 'not supported' and from what i've read there are several different 'types'.
In the future I'll stay away from 'TVs'
There's a thread discussing this issue and some people suggest it was a specific driver and was fixed after that vesrion, but I frequently updrate drivers and any time I check it's absent, regardless of driver version.
