Delete Unused Media from iMovie Library

I'm a youtuber and I use iMovie for all of my editing.

I make a new iMovie library for each video project. By "video project", I mean that there's usually a main video, but sometimes there will be some smaller related videos I make out of the same overall project. And if I can squeeze some short form, vertical videos, I'll make those too. So all of those videos will be in a single library. And when I'm done, I copy that library off to my video storage drive and on to the next project.

So here's the question. All of this stuff takes up a lot of space. And it can be hard to sort through raw footage in the Finder, so sometimes you have to just import it all into iMovie first, then sort it there. But the problem is, at the end of the project, I now have an unknown number of Gigabytes of unused media in my library. Clips that never got used for any projects within that library.

Is there some way I can select JUST unused clips, so I can delete them out of the library?

This would make my life significantly easier because reducing the size of every video project on my storage drive means I can fit a lot more projects on there.

AND knowing I can somehow select unused clips in a library means that I can skip even TRYING to sort clips in the Finder, and I can just immediately dump them all into iMovie and sort them there, where it will be MUCH easier and faster.