I've not worked with 360 video, so keep that in mind when reading the following comments
iMovie will edit 360 video and preserve its spherical format. If uploaded to You Tube, the website will recognize it as 360, but not sure if it will play 360 when exported to the desktop. Here's a link to a You Tube video that discusses editing 360 video.
https://www.youtube.com/watch?v=CzV0pSsx8sg
As I understand your post, you want to transform the 360 video into a flat video. Correct?
About 4 years ago I downloaded a 360 video from Vimeo and it played flat in the VLC app. So perhaps VLC did the conversion. Possibly it would work the same with QuickTimePlayer or the free download, Handbrake.
Possibly others who have personally addressed your issue might chime in here. I just wanted to respond to your post with the information that I had.
-- Rich