He has managed to fill the Nintendo Switch’s internal hard drive and our most recent microSD card.

This does not surprise me. However, I’m not sure if Nintendo themselves manufacture a card larger than this, and I’ve had trouble getting the Switch to… accept, for lack of a better way to put it, third-party cards (remember that whole trial and tribulation?), so buying a third-party card larger than this is a hell of a “maybe” to gamble on if you know what I mean. I’ll begin to do research on the matter, though. I have to.