To download iMovie 10.3.3 , you generally cannot find a direct standalone installer from Apple. Instead, the Apple Support Community Reddit users recommend using the Mac App Store to trigger a "last compatible version" download. How to Download iMovie 10.3.3 If your Mac is running an older OS like macOS Monterey
Locate it in your list of previously downloaded apps. Imovie 10.3.3 Download
Generally requires macOS 11.5.1 (Big Sur) or later. To download iMovie 10
If you're having trouble finding iMovie or a specific version, consider checking Apple's official support website or forums for more information. To download iMovie 10.3.3