This is the only config that managed to work for my setup:
AMD 9800X3D, Nvidia 3080 Ti, Gnome(Wayland), CachyOS
I still couldn't manage to make Hardware video acceleration working ( nor super resolution, which I assume is tied ) but this is at least better than the fallback to janky old codecs or plain black screen.
By using the following config thanks to these guides, videos are now properly decoded by the GPU ( as seen on GPU's video decode usage graph ).
Unfortunately, it doesn't seem like RTX super resolution is available for me.