iMovie to Instagram

What format is your movie and what format does Instagram want? Its help menu should tell you. Everything exported from iMovie is Mp4/AAC except movies exported using the Best quality (Pro Res) setting that will export a .mov format. If you have a .mov format then re-export it as an Mp4 that is almost a universaly compatible format.

Basically this is an Instagram issue, not an iMovie issue. Does Instagram’s help menu confirm that one can upload videos from a computer?

— Rich

Share (export) the movie to your desktop and follow Instagram's procedures for uploading the video to its site. The Instagram help menu should explain the procedure.

https://help.instagram.com/381435875695118/?helpref=hc_fnav

-- Rich

If uploading a video is not available from a computer, you might try air dropping the video from your desktop to your iPhone, and uploading it from there.

-- Rich