For the highest 360 video quality, professionals still use rigs, and for component cameras, full frame cameras offer unparalleled quality. The Sumo360 is a 3D-printed rig designed to be used with four full frame Sony A7S II mirrorless cameras renowned for their low-light capabilities.
Here is what the rig's base looks like:
The resulting video is up to 6k resolution.
One of the limits is that there is no genlock to synchronize the video from the cameras. Instead, Sumo's creators have relied on a clapper and audio syncing.
Sumo is licensing the 3D printing file for the rig for $359. You will need to use the file to print it at your own cost. The total price, including the cameras and lenses, is approximately $16,000.
Here is the official website.