I have roughly 60 other games for the Nintendo Switch besides yours and most of them have some sort of online element. If I’m not connected to Wi-Fi, I can still play those games; I just can’t access their online features. None of them force me to connect to the internet first before playing their offline modes. Despite having online functionality, I don’t have to EVER be connected to the internet to play Diablo, Super Smash Brothers Ultimate, Resident Evil Revelations, Resident Evil Revelations 2, Mortal Kombat 11, Dark Souls Remastered, and on and on and on.... Even Tetris 99 will startup and run perfectly fine without first being connected to the internet. It obviously just won’t find any matches unless the player has purchased the bot data DLC.You can kind of play offline on the Switch as the only time a connection is needed is to get past the initial login screen. From there the game should play exactly as if you were playing the mobile version offline - just don't completely close the game or you will need the internet connection to log back in again! Sounds strange, but it was a requirement if we wanted the online in the Switch version.
A broken product in the absence of the internet is not a “requirement.” It is a SOLVED problem. I’m not asking this to be rude or cheeky but have you actually tried Stack Exchange? Since literally everyone else has figured this out, there have got to be readymade free solutions that you can either adapt or use outright.
It honestly feels like you guys just threw the game on the Switch and then abandoned it. You clearly don’t even care that people in the US have never been able to buy the Witch Hunters DLC from within the game.