It sounds like you are looking for guidance on the file "iMovie 10.3.3.dmg".
Open the Console app on your Mac (found in Applications > Utilities). imovie 1033 dmg verified
Blackmagic Design’s DaVinci Resolve is professional-grade software. The free version runs on older Macs (macOS 10.14.6 or later). It has a steeper learning curve than iMovie, but it is 100% legal, safe, and more powerful. It sounds like you are looking for guidance