I don't know if it helps, but I just looked through a several Mini 3 Pro (not 4 but very similar lens and sensor) 360 panoramas on bright days (a big set of stills that would include every relative angle to the sun and then stitched) and didn't see anything like the kind of yuck in your Youtube video. There was flare but not like that.Here is some video from my Mini 4 Pro
Maybe contamination on the lens? Maybe poor lens assembly? It might be worth trying another unit if you really want one.