NewPipe [1] is an open-source alternative, although latest versions of Vanced will supposedly keep working for the foreseeable future [2].

[1]: https://newpipe.net/

[2]: https://nitter.net/YTVanced/status/1503055442506915846#m

And for AndroidTV devices, SmartTubeNext is awesome: https://github.com/yuliskov/SmartTubeNext