I find it very heartening that you’re putting this much care into avoiding harmful dopamine slot machines.
I think the proposed private-like solution is excellent. And I too would like to have a way to find my favorite photos from days and weeks past in a neat list.
However, this feels like two features. I don’t always want to communicate to a creator that I want to remember or like something they made. Only sometimes. And I think that a Like should be private to the liker and the poster and that the Favorite should be entirely private to the favoriter.