Yeah, Bell's Theorem or Bell's inequality states that there is a maximum bound between the correlations of particles in hidden local variable theories, which doesn't match with experimentation.

Superdeterminism is a loophole in this because it calls into question the ability of researchers to freely and independently choose their experiments. By changing this assumption, some superdeterministic models can violate Bell's inequalities. The problem is superdeterminism isn't really testable.

Edit: well let me rephrase that. Superdeterminism isn't testable right now. The only way to test this would be to rewind the state of the universe via simulation all the way back to the beginning of time and see if exactly the same things happen. We still may never be able to do this accurately enough to test, but I don't want to leave out the possibility.