As of now, inverse square law is the only way out for us. Einstein's GR is incomplete, he could not say what is curved space time is, what it consists of, how it comes into existence, and how it is responsible for gravity. For that there is no perfect answer for "what exactly is gravity".In my view, Newton’s inverse square law is not correct.An inverse square law is the only way you can get a stable orbit.
So it's pretty clear that any deviations from it must be tiny.
What I am saying is, as there is no choice we have to go for inverse square law.