Maybe someone does not know it, so I will just leave it here:

If you need to have a sliver or scroll away widget + sticky TabBar in a NestedScrollView, but you want to have independent tab scrolls in the same time, there is a solution in the flutter docs, please check it out:
https://api.flutter.dev/flutter/widgets/NestedScrollView-class.html#widgets.NestedScrollView.1