Is there actually such thing as a 2-128TB UHS-3 V90 A2 card though?
The SDUC standard exists, but no, there aren't any commercial 2TB microSD cards yet, though they're coming.
Is it possible to find a 1TB V90 A2 UHS-III SDXC card?
Not from a Jedi.
Everything except for the UHS-III part, yes. Some UHS-II stuff exists, but I think it's limited to full-size SD cards right now, and the Deck only has a UHS-I bus.
Is there actually such thing as a 2-128TB UHS-3 V90 A2 card though?
The SDUC standard exists, but no, there aren't any commercial 2TB microSD cards yet, though they're coming.
Is it possible to find a 1TB V90 A2 UHS-III SDXC card?
Not from a Jedi.
Everything except for the UHS-III part, yes. Some UHS-II stuff exists, but I think it's limited to full-size SD cards right now, and the Deck only has a UHS-I bus.