Move iMovie project to iCloud

You can’t. An iMovie project can only exist in an iMovie library, and an iMovie library cannot be stored in the cloud.

You can export the project to a movie and store the exported movie in the cloud.

— Rich

Export the movie to your desktop by clicking on the share button (the square with the upward pointing arrow in it) in the upper right hand corner of the iMovie project window, and then click on the File icon in the option box that appears.

Then open iCloud.com, sign in, select the iCloud drive icon, and drag in the movie.

You may need first to go to the system preferences on your Mac, click on iCloud Drive, and activate iCloud Drive

-- Rich