As of late, Steam users with Windows Mixed reality (WMR) headsets are able to play Shopkeeper Simulator VR with their devices!
With the kind assistance of a Steam user, it has been proven that Windows Mixed Reality (WMR) headsets are compatible with the game. Since I have no WMR headset, there was no official support yet.
According to his statement, however, a play area must be determined. With unlimited play area, problems with buttons can occur.
If you are looking to get into Mixed Reality, there are quite some headsets to choose from. Here is an article introducing the most important devices in 2019.