The game initially crashed under Monado using the Valve Index headset with the Valve Index controllers due to a missing hpmotioncontroller.json and vive_controller_presstomove.json files. Following another comment here, I copied the Moss Book II files from ~.local/share/Steam/steamapps/common/Moss Book II/Moss 2/Config/SteamVRBindings to ~.local/share/Steam/steamapps/common/Moss/Moss/Config/SteamVRBindings
After that it loaded just fine. However, I landed at a new controller mapping issue. I could use menu buttons and the analogue sticks, but it didn't see my trigger presses, so I couldn't start the game. Trying to open the controller bindings led to the following error:
Hit stubbed file at /home/[username]/.local/share/envision/opencomposite/OpenOVR/Reimpl/BaseInput.cpp:2511 func ShcowBindingsForActionSet
However, I switched to SteamVR at this point, and everything worked perfectly. Minus, you know, the several bugs with SteamVR itself. But the game was buttery smooth.