Hostile to quantum mechanics is the wrong way to put it. He was key in articulating it.

For instance:

https://en.wikipedia.org/wiki/Photoelectric_effect

I think it's fair to say he was dissatisfied with it (which drove his work on unification).

His work was foundational for the theory. However his later contributions to it was mostly detailed critiques. The critiques were brilliant and proved critical in shaping our understanding of the theory. (Even though Einstein wound up losing over and over again.)

See https://en.wikipedia.org/wiki/Bohr%E2%80%93Einstein_debates for a brief history.

There's really nothing like a determined and intelligent debate opponent for honing your arguments, and Einstein was immensely valuable in that regard.

Similarly, when Scalia died Ginsburg said she would miss his rebuttals to her opinions because they always made her final product better.

Sure, he produced work that was foundational to QM. I still think it's fair to say that he was hostile to the consequences of that work.