... Maybe: https://en.wikipedia.org/wiki/Pope_Joan

(She probably didn't actually exist, but it's interesting that until quite recently she was generally believed to have existed.)

Yes, that was satire, in Latin, John is spelled Joannes, or Joan for short.

What do you mean? Catcholic Church has records, did they just came up with something about a nonexistent Pope Joan out of thin air? How could they...

Catholic Church's records on early popes are often surprisingly bad, particularly in antipope-heavy eras. There are a _number_ of popes where the detail is pretty vague. Use of damnatio memoriae also confuses the issue, eg: https://en.wikipedia.org/wiki/Pope_Formosus#Legacy

eh not really, we NOW have quite good records on most popes except for the first few ones that we get just in a list from St Irenaeus (for example from St Linus - the guy immediately after St Peter - we get almost nothing)

but about the middle age popes we know quite a lot NOW. But it used to be different.