Maybe it is a TV settings thing. I’ve never messed with brightness or contrast much. It’s a new smallish 1080p tv. Vizio
Brightness/contrast were set right in the middle so maybe toying with those will help
I see the same issue with a Genesis through OSSC.
the picture with a PS4 on the same hdmi input looks good as far as I can tell. I’m not sure if that’s the best comparison?