OnStar isn’t GPS ,, it is simply old school high powered analog cellular service wrapped up in a fancy package... to get your position they would triangulate with cell towers... for joe six-pack sheriff to get that info would require a search warrant... there is no memory in the OnStar system that would retain your movements although it could be done at the provider level.
So Far so good...
BUT.... The FBI (and others) can listen in on your conversations through the cell connection without turning on the red “system active” indicator light... and they can do that in any GM car that has the OnStar equipment installed ; OnStars brains are built into the engine computer, if OnStar is available on your car and you didn’t order it BUT you have a radio with the little hidden microphone THEY CAN LISTEN IN!
If you don't want it, throw it away. Better yet, keep the OnStar and throw away the G.M. product.