SmartTube is, afaik, only for the Shield Devices and similar ddevices - so not really for Smartphones. Most of the time, it is great but for some reason I often get a network error message and the videos stop. So sometimes it’s annoying. Haven’t found a good solution yet

For smartphones, you can still download ReVanced. When Vanced was closed, they started again with revanced and it works like a charm. It has all premium features (like background listening) and blocks adds, even sponsored or fillers. The problem is the download, if you ask me. Because there is an official webside, but the download starts after it redirected you to some suspicious add website…

Alternatively, you can download NewPipe. If you don’t care that you can’t login, it’s a perfect app. In my opinion, it’s not really needed because you can save your profile (backup) and restore. It also blocks all the adds. Best app so far (IMO). It can be downloaded in the F Droid store.

For YouTube music, a good alternative is Kreate. Also available in the FDroid store.

If you have any further questions, ask me anything. Would be glad if I can help

Edit: NouTube is also a good alternative to YouTube premium, but I’m not really happy with the app. My complains are about some details though, so generally speaking, it’s worth a try