>>286990368
I found a fix:

>unplug headset
>restart steam
>VR button should be missing
>plug in headset
>click VR button when it appears
It only works once and the procedure has to be repeated every time. I've probably had this issue for a long time, but not realized because I keep the headset unplugged and close Steam, so I've effectively done it for months.

After looking it up, it is a persistent software problem that has existed for several years, with Vive too, it randomly occurs after owning the headset for a while, and there's no fix aside from buying a new motherboard. Annoying, but at least I have VR again. Valve really need to get their shit together.