“This miracle unified Muslims and Christians who had a devotion to Our Lady.” Couldn’t an apparition at a Catholic church also make Muslims treat Christians better? (Although it wouldn’t help the Coptics specifically as much.) Plus, Our Lady of Assiut doesn’t have the same counterargument (that I know of) because it happened in 2000-2001.

Re divine hiddenness - I’m not objecting to divine hiddenness so much as how it seems that doing the miracle on an Orthodox church seems misleading when there was a Catholic church conveniently available - I’ve actually seen someone arguing for Orthodoxy on this basis, so “the miracle will seem to the average person like vindication of Orthodoxy” isn’t a hypothetical concern. If non-Catholics are far more likely to go to Hell, doing miracles that look, to the people experiencing them, like proof that God approves of specific other denominations instead of sticking to obviously Catholicism-vindicating miracles is unexpected. Therefore, I think there being miracles across many different denominations is at least some reason to believe no denomination is super more likely than the others to be saved, even if the Catholic miracles seem more specifically vindicatory.

Of course, maybe the vindicatory nature of the Catholic miracles still outweighs there being miracles in a ton of different denominations - but this is why I think the mere presence of miracles throughout Christianity has a lot of weight.