There maybe something called open vr I believe for Linux, but I hardly did any research into it because I realised it wasn't complete, or at least for oculus use. The issue I've found is that the companies making the devices know how they work and therefore the hardware works best with there software, especially in the case of something like motion controllers, at least on oculus again. The final issue is where are you planning on getting the games to play if you can find a practical open source option? Nearly all of the main vr games are from the stores built into the companies software. Maybe a couple options, you could buy an oculus quest, only sideload games and never connect to the internet - not sure if this is possible. Or you could just use their software but ensure it isn't running in the background, and never connect to the internet when using it? I'm honestly not sure if it's possible to get away from their software, and honestly not sure its worth even counting as spyware at this point :D... Anyway I hope at least a sentence of that made sense lol.