Famous schizophrenia researcher E. Fuller Torrey recently wrote a paper trying to cast doubt on whether schizophrenia is really genetic. His exact argument is complicated, but I feel like it sort of equivocates between "the studies showing that schizophrenia are genetic are wrong" and "the studies are right, but in a philosophical sense we shouldn't describe it as 'mostly genetic'".

Awais Aftab makes a clearer version of the philosophical argument. He's not especially interested in debating the studies. But he says that even if the studies are right and schizophrenia is 80% heritable, we shouldn't call it a genetic disease. He says:

Heritability is "biologically vacuous" (Matthews & Turkheimer, 2022), and I think we would be better off if more of us hesitated to assert that schizophrenia is a "genetic disorder" based predominantly on heritability estimates.

I think about questions like these through the lens of avoiding isolated demands for rigor. There are always complicated ways that any statement is false. So the question is never whether a statement is perfectly true in every sense. It's what happens when we treat it fairly, using the same normal criteria we use for everything else.

https://www.astralcodexten.com/p/its-fair-to-describe-schizophrenia