V-r0cK on 15 August 2020
A quick google search would've solved this before you made the mistake in assuming New Mario Deluxe had online coop.
That's what I did even before reading your entire post and I found this right away....
https://www.co-optimus.com/game/5462/nintendo-switch/new-super-mario-bros-u-deluxe.html
"Online Coop = not supported"
