So, installed the Radeon Software Adrenalin 2020 / 19.12.2 drivers and thought everything was working fine at first.
On desktop, Windows has HDR enabled, monitor is in DisplayPort HDR -mode, HDR videos work etc.
However, as soon as I started first game the problems became apparent.
Overwatch, which is SDR game, for whatever reason runs the monitor in DisplayPort HDR mode in fullscreen mode, but it used to look just fine on earlier drivers (since the HDR got finally fixed in 19.10.1 or whenever it was). Now, it's all washed out and a bit darker.
Hellblade: Senua's Sacrifice, which is HDR game, was really, really dark. Toggling HDR off/on just made the screen freak out with overblown brightness (to the point almost everything burns through). The problem persists until a reboot.
Star Wars: Battlefront II, which is HDR game, wasn't dark, but instead it was overbright from the beginning, and again, problem persists until reboot.
I tried doing clean install with the new drivers, no help. Clean installing the previous set I used (19.10.2 I think) fixed things, but now I'm missing everything new in 2020.
Ryzen 7 3700X @ stock
16GB (2x8GB) DDR4-3600 CL16
ASUS Prime X570 Pro
Sapphire RX 5700 XT Pulse
Creative Sound Blaster Zx
750W Seasonic Focus+ Platinum
Windows 10 Pro x64, build 1909
Samsung C32HG70 (DisplayPort)