Are you getting a specific when trying to install it?
You can bypass this by temporarily disabling Gatekeeper via the Terminal. Open Terminal ( Applications > Utilities > Terminal ) and type the following command: sudo spctl --master-disable Press Enter, type your Mac password, and hit Enter again. Attempt to open iMovie. Once it opens successfully, re-enable your security settings by typing sudo spctl --master-enable in Terminal. imovie 1025 dmg install
Ensure your Mac is running at least macOS Catalina 10.15.7 ; version 10.2.5 will not run on older systems. Are you getting a specific when trying to install it
You can often bypass the need for a third-party DMG by using the : type your Mac password
Ensure you have at least 5-10 GB of free space, as video editing software requires ample swap space.