Looks like it was done in-house by Nintendo themselves. After DMCA-ing the crap out of YouTubers who post videos of the Steam Deck emulating Nintendo Switch games, as well as shutting down unofficial, fan-made projects that make use of their IP, I think Nintendo is finally giving their fans what they want: a proper port of one of their first-party titles on a platform other than their own.
It seems like Nintendo has finally given up the battle.
