Seems to need a bit of setup, but works well
The website for the game has detailed instructions on how to connect the app to the game (i.e. run the app on phone and watch, ensure it has required app permissions for heart rate and network detection, and THEN boot up Nevermind on PC). Those instructions even warn the user to press the stop button on the watch app so you don’t drain the battery. With this in mind, when this is done, this works as intended. The in-game biofeedback options does point out that disconnection (such as stopping and/or closing the app mid-game) may require a restart, so bear that in mind. For the record, I used the Steam version of the game, booted up in VR mode on a Steam Index. While I may have to reboot again to ensure that i can actually turn around using the trackpad (might be a glitch), that’s not relevant to a review for the Apple Watch app. So it does seem that the SteamVR version of the game is indeed compatible with this app, and after about 7-8 years, this app is still supported on iOS at time of posting.