I need the openxr app and I do NOT have access to MS Store  -  does anyone have the MS Store Product ID for this file or know a direct URL to download it?

Not at home right now but from memory OpenXR is an incorporated function. If you want to adjust settings such as resolution and reprojection you need to download OpenXR developers tool, this gives you access to the intrinsic functions of OpenXR. 

Thanks for the recommendation, I was just looking for a solution to a problem with the same problem.

Just to add to the confusion, as far as downloads, there is OpenXR dev tools, and OpenXR toolkit.  Different programs, both useful for MSFS.

OpenXR is implemented as an API/.dll, it's not an app.  Perhaps your looking for the MS Mixed Reality Portal app, which is a VR front end for using a Windows Mixed Reality HMD, or the OpenXR Tools for Windows Mixed Reality, which is a tuning and development app for WMR apps.  If you have Steam access, I think that their Windows Mixed Reality for Steam VR download includes the MS MRP app though not totally certain.  Other than that, not sure were one can safely get these apps outside of the Windows Store; MS is really tight on how it distributes is software.