How to fix controller input in Elden Ring Nightreign with Seamless Coop Mod

Got gifted a copy of Elden Ring Nightreign, but found that when using the seamless coop mod (for 2 player games), the deck controls would no longer work.

Anyways it turns out the solution is to set this as the launch options for the seamless mod executable:

SteamAppId=2622380 SteamGameId=2622380 SteamOverlayGameId=2622380 %command%

This makes the coop launcher be identified as the game itself, preventing any steam input issues. Note: if you seemingly get stuck on a steam loading screen after launching the game like this, you may just need to press the steam button and swap windows to the game.