I had some initial issues with making 3D videos work with VLC, so I went with the Stereoscopic viewer for a moment. But that had the sound from the embedded speakers being next to inaudible at the 100% setting: I had to resort to the ear phones I was trying to avoid for the more relaxed viewing.
But the issue seems to be Windows’ 11 reaction to the proximity sensor in the headset: whenever you mount or dismount the headset (e.g. to adjust an othervise hard-to-see or invisible setting on some options menue), it counts as a disconnect of the additional monitor and it had the headset revert from the 3840x1080 side-by-side resolution to the 1920x1080 mirrored resolution…
So when I set my computer to use only headset when in 3840x1080 mode and both monitors (or again only the headset) when worn in 1920x1080 mode, it finally worked as expected.
VLC was rather important because it’s the only player that allows you to put the volume at 200%, which was needed to get audible sound from most movies using the embedded speakers.
Please note, no Beam or Nebula involved: my main test system is an Intel Serpent Canyon NUC12 with an ARC 770m dGPU, because that has a USB-C Alt-DP connector (my workstations tend to have DP and I am still waiting for a matching cable from Amazon).