So many to choose from, but a recent favourite is NewPipe. Nice customizable interface, actively maintained, works reliably except for when YouTube changes things on their end (keeping up in a cat-and-mouse game with YouTube can't be easy!), and has good support for PeerTube too.
Just a few of the essential apps I'd recommend for android. All are open source and free of trackers last time I checked. All but the last two are on the play store. Most of them are better working and more privacy friendly than alternatives.
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