Does anyone know how to do anything with this?
The official documentation, (which usually provides at the very least a starting point for experimentation and discovery) literally says only this:
“Unreal Engine 4 now natively supports the Windows Mixed Reality (WMR) platform and headsets, including the HP Mixed Reality and the Samsung Odyssey headsets.
For complete information on installing and configuring the Windows Mixed Reality platform and headsets, see Microsoft’s Getting Started Guide.”
That’s it. That is the entire documentation about WMR in unreal engine.
There is actually MORE information in the 4.21 release notes (but still not enough to actually DO anything, and infuriatingly, the release notes link the the TWO SENTENCES of documentation as a suggestion for getting more information). The getting started guide linked here is the same guide you get when you plug in a WMR headset and it sets itself up, which is of absolutely no help at all in the context of getting it to work with unreal.
We are currently developing using the SteamVR method, but it would be really handy to be able to access the thumbsticks on the WMR controllers.
We’ve found the plugin and turned it on. Launching the editor still launches SteamVR. SteamVR still handles the interface between the headset and the engine.
Using professor google turns up the release notes, a bunch of sites with articles about the release notes, and a few posts here in the thread about the release notes.
Unreal officially natively supports WMR.