I hadn’t seen this frontend before. Its nice. Yeh quality selection does seem a bit buggy for me also (librefox). I see under the user settings (click account top right), there are some settings for default quality and mpeg-dash. I havent tested myself but just spotted them. Maybe try these ?
Edit: i skipped your mention of “installed “ viewtube. We may not even be looking at the same thing lol. Im looking at viewtube.io . Perhaps the same if youre selfhosting anyway.
Yeh its not exactly doing that for me. Just very flakey with manual selection of resolutions. My bandwidth is not a good test for the autoselection right now unfortunately. Need to test with and without DASH. Very promising though. Ive kind of given up on public invidious instances or similar so might be time to selfhost something like this.