Instead of my usual DL-DVI display, I connected a Samsung C27H711 via Display
Port. It officially offers 2560x1440 75Hz and the very same flickering issue
occurs.

I suspect the Polaris Windows driver has the same or a similar issue, as there
is sometimes black flashing when there is heavy VRAM clock jumping going on,
e.g. in games during loading screens or when watching videos with low GPU load
in mpv.