Constraints can be hard to see and even click on. I wish that when I was editing them I could see their icons much clearer, that I don't click on edges by mistake when I am trying to select a constraint because they are overlapping, and most of all see connection lines for highlighted constraints so I know exactly what they are affecting.
Sometimes when I try to add a constraint Fusion will tell me the sketch or edge is over constrained, but I just don't know where that error is coming from, because it's so hard to read the sketch/constraints UI.