It is not a secret that we don't yet have a final theory for gravity, and that is why, unlike the electro-magnetic force, currently there are still many alternative theories and conferences on gravity.
When I was a student in the 1980s, we were told that Einstein's General Relativity is the theory for gravity consistent with the Principle of Relativity. If one does not want to be brainwashed, perhaps one should read this article by G. B. Brown [Bulletin of the Institute of Physics and Physical Society, Vol. 18 (March, 1967) pp.71—77] and the book by A. A. Logunov.