this is one of the simplest posts I have ever read on your blog.

Thanks! The physics here is different and maybe easier to grasp as we are closer to what is generally taught at high-schools :)

If I am right, the issue is between relativity and quantum physics, right? What does quantum physicists/physics tend to gain by finding faults with relativity? Maybe I am missing something

The problem is that we have not found yet a satisfactory way to quantize general relativity. In the aim of finding a theory unifying all the four fundamental interactions, this however needs to be done. In all attempts made so far, predictions of deviations from the equivalence principle are made. However, this occurs at an even smaller level than the one probed by MICROSCOPE.

Does it make things clearer?