Nowhere near as good as Firefox on Android. That said you can get a clunky version with Brave. It's got a block and You can use use picture in picture to throw the video in the background. It sometimes pauses if you lock the screen but if you play around, there's a kind of race condition where you hit play again at the right time and it'll work.

There's also uYouPlus if you have a way to load apps without going through the store.