Installing iMovie from App Store on High Sierra 10.13.6
I've been running my Mac desktop for many years and having updated to High Sierra 10.13.6, believe it is as up to data as it possibly can be. I've just been introduced to using iMovie using my iPhone7 and finding the phone version fiddly, would like to be able to use my desktop to edit clips. Problem is that iMovie is not installed on my machine already and when I try to download it from the App Store, it tells me I need Mac OS 10.14.6 or later. I'm really confused what next to do. Please can anyone help advise?
iMac 21.5", macOS 10.13