When I change my refresh rate to 240hz my PC immediately black screens(sometimes with a RGB static block appearing as seen in the youtube clip). It then flickers making it unusable every second until the auto revert kicks in and puts me back to 144hz, where I experience no problems at all. I've thus far tried turning off freesync, upping the power limit % on wattman and checked all my drivers but nothing has given me any change/clue to what the issue is.
I've read online about the PSU often being the problem but I'm doubtful of that as mine should easily be able to handle my hardware. The computer and monitor are both under 6 months old. I'm using a display port 1.2 cable which I'm currently waiting on a spare to be delivered for me to test if that changes anything.
This is not my video but its exactly the kind of flickering that happens when i change to 240hz on my PC: