And this can even shed some light on the explainability of supervenience.

However, explainability is difficult to specify.

And is an epistemic notion like explainability needed at all to characterize an essentially metaphysical position like physicalism?

The perennial problem of the reductive explainability of phenomenal consciousness - C.D. Broad on the explanatory gap.

If emergence is a failure of the explainability of the supervenience relation due to a second component missing, then physicalism stays alive, because explainability is not an ontological issue.