Smarttubenext is a fork of smarttube. I believe it’s the only one that’s currently working.

I’m using it on Android TV devices and it works well. You do have to keep it updated or it stops working sometimes.

I use this on my android phone: https://github.com/InfinityLoop1308/PipePipe

I am assuming firestick runs some kind of android distro. From the project issues I see that some people try and run it on android tv so it’s worth a try.