This report details the likely origins of this request, the actual state of iMovie versioning, and the security implications of attempting to download files matching this description from third-party repositories.
People often hunt for specific DMGs like 10.2.5 when they are using an older macOS (like Big Sur or Catalina) that doesn't support the absolute latest version. If the App Store won't let you download it, check your "Purchased" tab to see if it offers a "last compatible version." Quick Review of iMovie 10.2.5
Are you trying to install this on an , or are you just looking for specific features that were in that version? How To Install iMovie on macOS [Guide]
A cross-reference of Apple’s official release notes and software repositories indicates a specific gap in the versioning timeline.
If you have previously "purchased" (downloaded) iMovie, you can often trigger a download of the last compatible version directly from Apple: and click your profile name at the bottom left. in your purchase history.