Unable to move certain videos from Photos to iMovie on iPhone 14 Pro

The immediate task is to drag (11) videos each 5min or less, into an iMovie project.

I have learned that the drag-drop is ignored without any feedback, if you try to drop into iMovie's project media area. Kinda lame, since I don't want to place my vids directly into the project, I just want them in iMovie library so I can delete from Photos. Stat!

I discovered that I can drag and drop to the movie timeline, but of the (11) I try to move, only (6) reach their destination. All but (1) is landscape format, and all are the same file type taken on my same recent iPhone 14pro device.

I tried to drag and drop directly to the finder window revealed when I select a media item in iMovie and then File>Reveal in Finder. I think I'm able to drag-drop copy out the same (6) out of (11) total items (haven't matched up file names to be sure, but it's about the same number). I've had this issue before where random videos in Photos won't play or won't export. Waiting for iCloud to sync maybe has gotten around this? I can't remember now. The whole process of moving. a. simple. file. has gotten so mysterious I'm kinda done.

This is really clunky and glitchy. How do we make it better?

[Re-Titled by Moderator]