TLDR: NewPipe 0.27.6 fixes the YouTube issues by performing the integrity checks now required by Google; NewPipe is being refactored heavily on the refactor branch and you can help and provide feedback on a nightly version; NewPipe will soon have a new completely rewritten player; the NewPipe team is struggling to keep up with the project’s demands due to dwindling free time of its members.
I haven’t been able to get ReVanced working for a while. This is a standalone app that let’s you watch YouTube without ads and plays while the phone is locked?
Yes, that is correct. It also has support for peertube, SoundCloud, media.ccc.de, and bandcamp.
Greyjay?
Not open source but source-available and trying to push alternate platforms.