We don’t know for a fact that QM contains irreducible indeterminism. If many worlds is true, then QM is ultimately deterministic. Same if hidden variables is true. A large class of local hidden variable theories have been ruled out by Bell’s theorem, but non-local hidden variable theories survive it (such as the Bohm interpretation and the transactional interpretation), as do local hidden variable theories which deny the Bell theorem’s assumptions about the nature of measurement, such as superdeterminist local hidden variable theories.