Not-yet-falsifiable beliefs?

I recently encountered an unusual argument in favor of religion. To summarize:

Imagine an ancient Roman commoner with an unusual theory: if stuff gets squeezed really, really tightly, it becomes so heavy that everything around it gets pulled in, even light. They’re sort-of correct—that’s a layperson’s description of a black hole. However, it is impossible for anyone to prove this theory correct yet. There is no technology that could look into the stars to find evidence for or against black holes—even though they’re real.

The person I talked with argued that their philosophy on God was the same sort of case. There was no way to falsify the theory yet, so looking for evidence either way was futile. It would only be falsifiable after death.

I wasn’t entirely sure how to respond to that, so I just indicated that this argument may be proving too much. However, it genuinely is possible for a true theory to exist that we simply lack the ability to test. Do we simply have to accept that it’s impossible to learn about such things? That seems like the right answer, but it feels unsatisfying.

Any thoughts?