I want the latest version of imovie.

The most recent version is iMovie 10.1.12 and it requires macOS 10.13.6 or later. So you shod be fine, when you download it from the main tab of the App Store.

There's no path to update from version 8.0.6. Try going to the online app store and obtaining current version for free. Type in iMovie 10 or something like that in the search box.

-- Rich