This is one of the first things I noticed when I started using GrapheneOS. When trying to change the volume via the volume slider, it always jumps to the position of my thumb instead of just sliding up/down from its current position with the thumb, which often leads to me setting the volume way too high by mistake.
I think this is the default AOSP behavior, I am not sure if its the same on the Pixel stock os, but it is very unintuitive. I hope this is something that can be fixed (or maybe it already is in QPR1?).
I think OneUI and iOS behave similarly to the behavior I expected.