You can’t really replace YouTube’s massive library yourself, the best you can do is avoid it but that’s hard too. As for the frontend, there is
NewPipe/Tubular (Android, also supports Peertube, media.ccc.de, SoundCloud, Bandcamp)
Piped (web, very privacy-friendly)
Grayjay (Android and desktop, partially open source, support for many services including PeerTube and Odysee, $10 or guilt-tripping infinite free trial)
You can’t really replace YouTube’s massive library yourself, the best you can do is avoid it but that’s hard too. As for the frontend, there is