Could you check whether all of these codecs are installed?
ffmpeg-4 lame gstreamer-plugins-bad gstreamer-plugins-ugly gstreamer-plugins-ugly-orig-addon gstreamer-plugins-libav libavdevice57 libdvdcss2 vlc-codecs
Do you see any difference in the videos you play on vlc in Ubuntu vs on mpv in Tumbleweed? I mean quality wise or artifacts.
Note: I just copied a list of common codecs. Not all of them might be necessary for your case.