DennisLeonn-
You have gone beyond and above. Thank you.
Turns out none of the tests I set the user worked. Out of desperation, I asked them to check their OpenXR runtime and to switch it to steamVR OpenXR runtime. That cleared up the problem. Apparently, one does not need Vive OpenXR plugin. That is, as you said, the VRTemplate w/ just OpenXR plugin active is good for Quest (2/3), Valve Index and Vive. The latter two require steamVR OpenXR runtime. The former seems to be happy with either steamVR OpenXR runtime or Meta/Oculus OpenXR runtime.
This is what I expected.
Learnt a lot, appreciate that and your help.