Yes — so much so, they added it as an extra assumption to their model. The original justification is that we have things like Bell’s experiment that say realit

Yes — so much so, they added it as an extra assumption to their model. The original justification is that we have things like Bell’s experiment that say reality is non-local or non-deterministic, because they exclude local determinism. But since then, we’ve found increasing evidence that it’s non-local, and so the choice made for the Copenhagen interpretation, to preserve locality at the cost of determinism, becomes unjustified. It’s now included as an extra assumption out of tradition, and because no one wants to seriously rewrite things. However, as Smolin contends, that may be a dead-end intellectually and an impediment to unifying QM with relativity. A non-local, but real QM interpretation has a more straightforward paradigm to merge with relativistic gravity: it aligns their models philosophically.