The fact the quantum mechanics is nonlocal is known already for a long time, since the Bell works (1966 and later) and the Aspect's group experiments confirming the Bell-type CHSH inequality (1980 and later).
More exactly, it was proved that there are results, obtained in experiments with entangles particles, that cannot be explained by local distribution of variables. To put it simply, it seems that during the measurement carried by Bob it is known what measured Alice (or if she measured), and vice-versa.
(Note: After the experiments testing the Bell-type inequalities, in the years 1990 and after that, there came proofs so-called contextual: mainly, Hardy's paradox and the GHZ experiment. They proved the non-locality without hidden variable distributions, per single experiments. But these experiments seem to do more, they even cast doubt on the possibility to explain entanglement results with non-local, deterministic hidden variables.)
But, this result cannot be exploited for performing FTL (faster-than-light) communication.
What is the most general proof for this statement? Has it something to do with (does it rely on) the QM?
One proposal: a machine able to transmit FTL messages, appears, from the point of view of some frames of coordinates, as a machine that transmits messages backward-in-time. Well, at least in our part of the universe, we cannot change the past. I consider this as the most basic argument because it doesn't rely on QM, or thermodynamics, or other field of the physics.
Are there other suggestions for a general proof? Could it be that we can't prove the no FTL communication without arguments relying on QM?