When trying to detach audio from a video clip, there are no audio bars in the green track. The video does have audio when I play from my computer downloads. Any ideas why?

It might be a corrupt iMovie preference. Try deleting preferences and see if that solves it. Open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen

your old library to get back to your projects.  Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.

If no luck, make sure that your software is up to date.

Also, it might be that the video sound is not in a format that is compatible with iMovie. iMovie likes Mp4/AAC. Try converting your clip to H.264, Mp4/AAC with the free download, Handbrake. Do that even if the codec already is indicated to be Mp4/AAC. Re-rendering often cures the issue.

You can get Handbrake here:

https://handbrake.fr/

A simple way to do it is to open Handbrake and do a File/Open Source. Navigate to your video and choose it as the source from the resulting screen. Then do File/Start Encoding. Wait a couple of minutes for the conversion to complete. Then save and import the converted clip into iMovie.

-- Rich

Another thing that you can try is to create a new project and see if the sound plays fine there.

-- Rich