My MacBook imovie somehow imported my entire photo and video library and will not allow me to delete them. Help!

I am not sure what I did, but while trying to import only the media items I would use in imovie, my entire library is on iMovie. When I try to delete in the Media tab: I highlight a photo and right click on it and all it says is "reveal in Photos".

I do have iMovie on an external drive but it's frustrating having over 1000 photos/vids to claw through.

I have unlinked iMovie from iCloud hoping that would work: no.

Will I need to wipe the whole iMovie clean? Can I do that?

Sigh. Thank you in advance!!!