Vertical video in iMovie: green screen doesn't work when adding over a video background
Working on a MacBook Air, most recently downloaded iMovie. Trying to create a virtual short video for a real. I have a video background added to the iMovie and I have a pre-recorded video recorded with a green screen. However when I add the green screen video, the green/blue screen doesn't apply. No changes appear. Because it needs to be vertical, I'm working with "New App Preview" type project.
MacBook Air 13″, macOS 14.3