SmartTube is excellent for ad-free YouTube. I've seen others recommend TizenTube, which more closely follows the official YouTube app aesthetic, but to be honest, I prefer the more minimalist look of SmartTube. The fact that it can also play Shorts (where the official YT app tries to push them to your phone) is a nice bonus.

One downside for those who use it: "Free with Ads" movies on YouTube will not play on SmartTube for some reason.