How to recover missing iMovie files after transferring from old iPhone to new iPhone?

I recently got a new iPhone. I transferred all the files from the old phone to the new. I never used my iPhone with iMovie and only used it for taking photos and videos. I had created well over 100 iMovies over the past few years. I have used my iPad to do movies with my videos. I backed up my photos from my old iPhone onto my Mac prior to the transfer. Now, my iMovies will not come up stating that the files do not exist.

I've tried to research a fix but nothing works. Any suggestions? All that work and memories are gone.

[Re-Titled by Moderator]