The question of how can the Equivalence Principle work in the presence of gravitons comes up surprisingly often! You will enjoy this discussion https://physics

The question of how can the Equivalence Principle work in the presence of gravitons comes up surprisingly often! You will enjoy this discussion https://physics.stackexchange.com/questions/589074/why-can-t-gravitons-distinguish-gravity-and-inertial-acceleration https://physics.stackexchange.com/questions/589074/why-can-t... They go over several reasons why gravitons don't break the equivalence principle. In particular the answer about virtual particles is very important.