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)
Instead of using YouTube, use PeerTube
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