I made this thread about how to do this on the official SE boards a couple years ago, and nobody uses those any more apparently, but here's the gist of all that:

1. Go into SE settings > Display and change the view from "perspective" to "cylindrical".
2. Set the windowed screen resolution in SE to 3216 x 1608 for a resulting 4k 360 video.
3. Export MP4 video.
4. Inject the 360 data into the resulting MP4 with the Spatial Media Metadata injector tool.
5. Upload the tagged 360 MP4 to YouTube
6. Download the full-resolution 360 encoded VR video when it's done processing.

https://forum.spaceengine.org/viewtopic.php?p=39426#p39426

And here's an example video. Be sure to select the highest resolution, it makes a big difference!

https://youtu.be/gs0Jst0R_XM