I remember reading somewhere that Nirn may have an infinite (or vast) amount of continents. Can anyone confirm this?

I think you may be confusing continents with planes. there arent that many continents in Nirn.

Indeed Nirn cant have infinitive amount of continents if we watch it as a planet like we have them in our universe.

And I think you have misread or something about that Nirn could have a vast amount of continents as we probably dont know every part of the planet yet.