I haven’t dug into it deeply so I’m sure there is more in the backend too, but on the visual side it’s gotten a slightly modernized redesign and support for Material You. But from a user perspective one thing I’ve noticed is the actual video player seems significantly smoother and particularly switching between picture-in-picture and fullscreen and back seems a lot smoother (which I do a lot).

Overall it’s just like PipePipe but better. As someone who’s been using PipePipe for a long time there’s really no reason not to go straight to PipePipe-X. You should be able to import your user settings and history straight from NewPipe too.