I updated to MacOS Monterey and now my iMovie gets stuck on load the library

The problem that you mention has been reported by several others on this forum. It appears to be an issue related to Monterey and iMovie. Some conflict or incompatibility. None of the commonly used diagnostic procedures have resolved it. Hopefully Apple will soon resolve it with an update.

Meanwhile, let the library load overnight, or for as long as necessary, as others have reported that the library will eventually open. Possibly, after the first time, the iMovie library will load normally. You can also try opening iMovie in a newly created library. To do that open iMovie while holding down the option key and select to open in a new library. You can also try opening iMovie in your Mac’s guest account.

— Rich

I often leave iMovie open on my doc so I can access it quickly without having to load the library each time. Until Apple fixes the slow loading issue with Monterey, possibly that method would be a temporary workaround.

-- Rich

FCP X also appears to have the same problems.

Were you able to get the library to open?

-- Rich

EDITED BY POSTER: You can disregard this post as I received yours that crossed with mine.

A comment on the Final Cut Pro forum suggests that all libraries take longer to load but the larger the library, the longer the wait.

I am experiencing the same issue. It takes 30 minutes to load a library for a short video. It's ridiculous.