System spec - Ryzen 3700X CPU - AMD RX 7900 XT GPU

I got an AMD GPU specifically because I wanted to switch to Linux. I've done a bunch of testing over the last year while I still had an nVidia card. Now I've got an AMD GPU I feel ready but it has not gone well.

When I use multiple monitors I get a range of odd behaviours, including a white screen, lock ups, failure to display anything on second screen. I've unplugged the second screen for now and all is OK except that adaptive sync does not work properly.

When I set adaptive sync to "Always" in the settings the screen sort of flickers when I move the mouse. To be more precise the screen gets a bit brighter when the mouse is moved, then returns to previous slightly dimmer brightness when the mouse is stopped. There are no errors that I've found.

Both of those issues happen in fresh Fedora 38 and Arch Linux installs. I'm running KDE-plasma (using Wayland not X) so it seems like a KDE issue. Though I'm about to test it with a Fedora and gnome install next, though I doubt it will be any different.

EDIT: Small update. Running Arch/KDE. I have found I can get it sort of working. I boot the PC with a single monitor (my 165Hz ultrawide) and set it to 60Hz, then turn on the second (1080p 60Hz) monitor. At this point I can set the then changing the ultrawide to 165Hz and set adaptive sync to automatic, but I have to do this process everytime I turn my PC on. Also, if it goes to sleep or I want to shutdown/reboot it goes mad again and things lock up. I have to turn off the second monitor off before I reboot/shutdown, or before I goes to sleep. Then I have to go through the whole process again. Obviosuly not ideal.

EDIT2: Turns out it was the old LCD I was using as a second display. It has been around a very long time, and while it always worked OK it clearly doesn't like something about how Linux talks to it. Anyway it is working now. Though Adaptive sync on the desktop is still flickery.