This has happened to me many times in the past and all the methods i came across dont seem to work. But i have a solution: screen record the recording, what i mean by that is open up photos and screen record (like usual) the video you wish to use in iMovie, so you double screen record. It can be a bit tedious but it’s the only way you’re gonna get audio in iMovie with a screen recorded video. Sorry if this didn’t make any sense but i hope i helped :)

This has happened to me many times in the past and all the methods I came across don't seem to work. But I have a solution: screen record the recording, what I mean by that is open up Photos and screen record (like usual) the video you wish to use in iMovie, so you double screen record. It can be a bit tedious but it’s the only way you’re going to get audio in iMovie with a screen recorded video.