Are you talking about Half Life: Alyx? It works on basically any VR headset as far as I know. I think they just need to be SteamVR compatible which basically everything is.

Just to confirm, you are correct, it works on almost any mass-market headset (probably on all headsets period, but I cannot verify that myself).

So far, I can confirm for a fact it works on HTC Vive, Valve Index, Oculus Rift S, and Oculus Quest 1/2 (in wired mode connected to PC, just like the other headsets, or using VR Desktop for wireless; I tried both and stuck to playing it with wireless).

Maybe, as soon as I heard it was VR only I stopped paying attention. But the point still stands - Valve is very much a hardware business, has been for years.

I wouldn't characterise them as a hardware business, their main focus is on software and they happen to be willing to produce hardware when they feel they need to.

I've played Alyx three times on two different VR headsets by two manufacturers and this is definitely not true.