The holy spirit is a funny exception, since it doesn’t have an actual name, but this still feels right, even there.

The sun and moon are other examples. Historically there’s no reason to have a name for them, since they’re the only one. Sol gets called Sol in some contexts now, and there’s Luna, but that hasn’t really caught on - it’s usually “Earth’s moon”.

You can definitely talk about Popes plural, if you don’t just mean the current one.