iMovie is utterly and completely not responding.

iMovie... what has happened?

I use iMovie at least weekly to edit medium-sized videos. Not complicated production, just simply clip, title, open screen, close screen. iMovie has worked extremely well for this for years.

Along comes the iMovie 10.4.4 version and MacOS Tahoe (26.3.1a), and iMovie, literally in an instant, became completely unusable.

Launch iMovie as usual - it launches almost as fast as always. But that is where things change. Whether I open an existing project or start a brand new, blank project, the same thing happens: an immediate spinning rainbow ball of doom. A very small clip (1 minute or less), the spinning ball takes 20-30 minutes to return to "responsive", which of course goes back to the spinning beach ball of doom as soon as I click on the media itself.

Or - I can start a new project and drag a large video file in - and the same happens... except the app is unresponsive for an hour or more.

I would understand if maybe my M1 Mac with 1TB SSD were at capacity (the drive is full). I could understand somewhat if I had a dozen apps and other projects working at the same time.

But even with ONLY iMovie running, the exact same thing happens.

Activity Monitor simply stays listing the top resource hog as iMovie, with iMovie (not responding) in red text, and the processor using 120-164%.

I have followed as many troubleshooting suggestions from both official Apple Channels and others - everything from resetting the preferences, removing/deleting media, removing the iMovie library file, rebooting in Safe Mode, deleting iMovie completely and installing a fresh copy from the App Store... At one point, I actually got beyond adding a video file to a new project, then added a small image as an opening screen, but then the behavior came back moments later.

No other apps, whether resource hogs or not, are acting this way - literally EVERYTHING else is running absolutely normally. And they continue to work normally even if iMovie is sitting and spinning in the background.

I have reported this via Feedback Assistant. But otherwise, I am at my wits' end. I am really not thrilled about having to migrate to an entirely different software/app solution..., but at this point, I am functionally dead in the water.

Simply having iMovie OPEN (no project even selected or active) shows %CPU at over 100% sitting doing NOTHING!