Discussions using the word ''supernatural'' will often amount to nothing if the definitions aren't agreed upon in the beginning. We can see it here in the exchange between JUC ans straggler where they obviously aren't using the same definition of 'supernatural'.
I have always tried to define supernatural along the lines of ''outside of nature''. Nature here being our multi-dimensional universe. An alternate definition would be ''everything that is not bound by the laws of nature''.
The christian God would therefore be supernatural according to this definition. Ohter universes in a possible multiverse would also become defined as supernatural, however. This could make some sense in the way that even if these other universes interacted with ours, not being bound by natural laws, this would appear like some kind of 'supernatural' interaction from our point of view.
This definition therefore also allows for interaction between supernatural and natural, without the former becoming the latter because of this. and this interaction will be detectable/observable, although not scientifically detectable because it cannot be repeated as a natural phenomenon could.