rt, by the way, I haven’t visited unity official site for long (over a year?). It has changed a lot!!! so I am not sure I ask questions in the right places.
Finger dragging is just a form of input, so yes, plenty of “sources” for that. Start with the Unity official finger drag / touch tutorials, maybe branch out into Youtube tutorials for touch / drag.
“Water flow post effect”… I have no idea what that might be. You may wish to find a game that does such a thing and refer to that.
like liquid effect, when I drag over it, it bends and flows.