Unable to use iMovie on Montery??

Instead of using the Updates feature of the app store, try this procedure where you can download iMovie from the purchases list in your app store account:

To update/redownload iMovie 10, drag your iMovie 10 app from the Applications folder into the trash, but do not empty the trash. (You can skip that step if you had iMovie 10 on your computer before, but deleted it.) Sign in to the app store and open your purchases folder by clicking on your name at the bottom of the app store side bar. You will see your purchases displayed, including iMovie 10. Redownload/update iMovie from there. If not successful, drag your present iMovie app out of the trash (if you moved it there) and return it to the Applications folder.

-- Rich

I believe early versions of Monterey may have caused problems.

Have you got the latest version 12.4?

You could try deleting the preferences by holding down the Option and Command keys as you try to launch iMovie.

In the window that should appear, click on Delete Preferences and iMovie should open.

Etrecheck is a diagnostic utility by etresoft, a respected member of this community.

You can download it free from the respective website.

It produces a report that will let us look for possible problems.

Without it, we can't know what may be installed that is causing this.

You can browse this forum and you will find hundreds of Etrecheck reports.

And of course you can look at the report before you post here, and see that it does not convey any personal information.

This looks like you may have a pesky "antivirus" blocking your downloads...

Also, as you say you have upgraded to Monterey recently, there may be old stuff in your installation that is not working ok in the new OS.

Please run Etrecheck and post its full report here. Use the "additional text" button and paste the report into the text box.

Download EtreCheck here. https://etrecheck.com

It is free and perfectly safe.

It takes several minutes to run and checks everything on your computer. Luis is good at reading the results and spotting possible problems.

I take it that you are using the AppStore correctly?

Click on your name and the Updates heading in the left column to reveal iMovie etc.

Shut down your Mac and remove the mains electricity plug for a minute.

Then start up the Mac and see if that helps.

What happens if you take the app from the trash and put it on the desktop?

Can you do that?

Sorry, I thought you were on a Mac Pro.

So just shut down and start up again.

Sorry! Just realised you said the app is incompatible with Monterey and you can't download a new one.

I'm sure someone else will be able to help you with the AppStore problem when the US wakes up.

Why can't you just open the trash and drag it to the desktop?

Then you can put it in the Applications folder.