topic says it all - the question is if the GOG version has VR support like the Steam version, especially if it supports WMR hmds.

There is what the "Readme" files says for the GoG version:

"3. VR SUPPORT

Overload works with the Oculus Rift and Vive VR headsets on Windows.

The batch files OverloadOculus and OverloadOpenVR are provided to start
the game in VR mode. Or if you're running in Steam or Galaxy you can
use the VR launch options provided."

There people on Steam have been talking about the game working with WIndows Mixed Reality.