Update: Chat with Polycade is good when they finally get to you since they shipped a lot of orders. Good news I got it working! The bad news is that Polycade can't control the analogue stick of the Switch, which certainly restricts which games work. The Sente's 8-way stick essentially controls the Switch's D-Pad. So if the game you want to play works with the D-Pad for navigating menus and the game itself...it works. For example, I got Mario Kart 8 to work, but not Mario Party Superstars. But a lot of the Nintendo online subscription games do work bc they're old school (NES, SNES, GENESIS).
While Mario Kart 64 on the Nintendo Switch does't work...I used the built in N64 emulator on the Polycade to run a ROM of MK64 and remapped the analogue stick to the d-pad so the Sente did work! So, there's some cases where if you can get the game for emulation, you re-map the controls (I had to learn how to do that with RetroArch, which is built into the Sente by pressing F1). Honestly, not that hard to do.
