Hi! Sorry for the late response, but I managed to fix the issue like this:
My HDR monitor (2k resolution) is connected via DisplayPort and running at 165 Hz, while my SDR monitor (FullHD) connected via HDMI and running on 75 Hz.
1, I checked on what refresh rate the monitors are running, and the first is SDR ran at 59,999 Hz instead of 75, changing this still not fixed it for me.
2, I tried to lower the refresh rate tho 60 Hz on my HDR monitor, and the HDR-SDR combo with HDR enabled started to working, BUT
3, for some reason the resolution went down on my HDr monitor, so I change it to something else, and back to my 2k resolution on my HDR monitor
4, Restarted the computer to check if it is working and since then it is working perfectly
Hope it helps you too. I have the same GPU.