exact same problem here!
not only instagram but also in youtube, quick apps. I just show this to a tech support at apple and they said it “should” be a software issue but they arent completely sure.
after that I did some work by myself and found out how to fix it for now.
go to setting-camera-format
and change the format from
high efficiency to most compatible
if you do that, you wont be able to shoot videos with the whole new HDR function and 4k 60fpms
but when you upload your videos on the third party apps such as instagram, youtube , it will look just fine.
it is just for a temporary hot fix that I found out.
my question is still there are some
youtube videos people uploaded few days ago with 4k 60fpms with dolby vision out there but how the hell their phone works and mine doesnt.
it seems for some iphones it is fine but for someone elses like mine and yours arent.
anyway change the video format for now till they fix.