If you don't know, update 1.2.0+ allowed Pokemon from the IOA to be traded to SwSh without the DLC. What happens if in surprise trade, someone put a(pokemon not in base game)in surprise trade and the other person doesn't have update 1.2.0+? Would it crash? Would the game not choose that person? Or is it required to get the update which means the scenario can't happen?
For any Nintendo Switch title, your game must be updated completely to access the internet. I know this from experience from multiple games including Pokemon.