Unless there’s a way to stop the Deck from adding controllers internally, not at the moment.
A friend who has a Steam Deck only has that issue when its docked, so I don’t know what’s causing it.
Bummer but I've been loving how quick and fun the game is. If I'm able to in game manually choose CPUs and players than I bet that would fix that but I get that's a lot of technical work behind the scenes.
Keep the grind going! Loving this game! Would love to eventually see this game on Steam but totally get if that's not in the cards.