Sorry if I have missed something obvious. Due to my special VPX setup (Windows running in Parallels Desktop on a Mac computer) I think I am not able to get the SteamVR working, which I believe would be the default approach. However, should I be somehow able to get my current VPX installation to work in VR by utilizing OpenVR or OpenXR? If so, what steps should I follow? I would also like to verify, is this the proper link to download the Visual Pinball VR: https://sourceforge.net/projects/vpvr/
Thanks
If you are still having issues, no Sourceforge is not the correct place to download VP VR, it has old software and you are correct to grab the RC3 build from Github that you did with your second post, although you should probably update to 64bit as most newer tables require it.....and RC 4 is now available. Using the openvr_api64.dll that comes with the GL.exe build v1947 will require you use Steam VR. You did not say what headset you are using but to run without steam you would need the new .dll from Gitlab (Mike posted a link, scroll down to "per game installation) to replace the one that comes with the GL build and rename it to openvr_api64.dll (with a 64 in the name) if running 64 bit. Then Virtual Desktop (the standalone version) and it's streamer with the OpenXR Runtime set to VDXR. That said, I don't know if any of this will work with your "Special VPX Setup" 
Thank you very much. I think I advanced a little. I now tried the latest VPinballX_GL-10.8.0-1975-051104c-Release-win-x86.zip (I remember someone saying the x86 could be more stable or similar, but I could remember wrong). Then as you said I downloaded the new openvr_api.dll from Mike's link above. Then I installed the Virtual desktop streamer, set the OpenXR Runtime to VDXR, but the Virtual Desktop itself came from the Steam. It was the only source I was able find at the moment, and I think it might be wrong, because it always launches the SteamVR which fails as usual. However, when I start the VPX, at least I am not seeing the vulkan dll issue anymore. But how should I continue, another download link for the Virtual Desktop perhaps? I am still a little bit lost with these multiple software, like what purpose do they serve, or at least what is the actual starting order and so on. And oh yeah, I have Nreal Air glasses. They have worked great with the VPX in the static side-by-side 3D mode. I am able to get the 3DOF head tracking into the Windows using the PhoenixHeadTracker. I am also able to forward the 3DOF motion information forward into the Opentrack, but I am not sure are these two software needed at all. The PhoenixHeadTracker is able to output Opentrack UPD, or directly move mouse on the screen. Anyhow, I would first like to get the Virtual Desktop approach without the SteamVR into its defaults state. Then if I could see some signs of VR life, I could start to hassle with the head tracking. Many thanks to all your kind help!