iMac not downloading imovie on Monteray 12.7.4

Go to the Mac App Store > click on your Account (bottom left corner) > select the version of iMovie that is in the Purchased section > then open or download from the cloud.

see "How to redownload apps on Mac" at > Redownload apps and games from the App Store - Apple Support

Was Monterey recently installed when you first had this problem? Have you previously used iMovie on this particular iMac?

Apple does not allow old versions of their free software to be downloaded unless that software (version?) was previously installed on the Mac in question using the Apple ID in question. In this case you will get a popup message that the current version is incompatible and ask if you wish to install the newest compatible version.

It sounds like you may be downloading a really version that was once part of an iLife purchase bundle used on a previous mac which is not compatible with Catalina/newer.

Check your Applications folder and see if you have the iMovie 10.3.8 iMovie version for Monterey 12.7.4.

If not, keep checking the Mac App Store for Updates.

If iMovie isn't working on your Mac - Apple Support

Now check for Updates in the App Store.

Hmm.. try starting up in Safe Mode followed by a normal restart and then recheck the App Store for Updates.

see > Use safe mode on your Mac - Apple Support