Is there any workaround for this? I don't seem to find default app for this, I don't know if this work similar to pick the default browser. Any ideas to try? What bugs me is that smart YouTube tv is that it doesn't show history, so it would be easier to see the videos without manually typing.
Disable the native you tube app
Go into settings on SmartTube next and select casting, it’ll allow you to link the mobile app directly to the SmartTube app and any casts will go there
then you have to link with the code of the official YouTube app on tv. and when you press cast button in YouTube on mobile app you will see cast YouTube on TV select it. good to go
Be sure you're using SmartTubeNext, not the deprecated SmartYoutubeTV.