iMovie does not open after installing Monterey

What happens when you try to open iMovie? Any error message?

A few things that you can try:

1. Update iMovie to current iMovie 10.3.1.

2.Open iMovie in a new library, by holding down the Option key while opening and creating or selecting a new library from the box that appears.

3.Delete preferences by opening iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects.  Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.

4.Boot up in Safe Mode (see Finder menu for instructions) and, after everything loads, immediately shut down and reboot in normal mode. Then see if iMovie will open.

5.Try resetting the System Management Controller (but no longer available for the new

M1 computers):

https://support.apple.com/en-us/HT201295

6.Try resetting the NVRAM or PRAM,.:

https://support.apple.com/en-us/HT204063

-- Rich

Had the same problem and found a solution: double click on your iMovie library in Finder app. Started iMovie without any problem. Hope it works for you, too!