edit: There's also an 8MB game about Trains, with some short videos and hi-color images in there.
But if you wanted to let a DMG address 2 gigs of memory 32k at a time you could do it.
It’s a little hard to imagine a game needing > 1MB if it’s just B&W. But I suppose you could put a ton of text in or do some kind of demo-scene style ‘video’ playback. But no one would have for cost reasons back then.
Not on the GBC, but GBA had a number of video cartridges, including several full-length movies:
You can't freely mix the first 128 with the last 128 but that's easy to deal with.
I think that it would be literally impossible to have random access memory of 2G.
For these paged systems, you typically swap in the the page you're interested (iirc, gameboy did it by writing the page number to particular memory addresses) and then work with it for a while, and often execute code directly contained in it, which will eventually lead to loading the next page you need when you need it.
One of the common mappers even enforces that you may not pick bank 0 for the switchable bank, picking 1 instead.
Mappers found in bootleg multicarts do allow you to change the base address and size of the game, which will move the fixed bank.