iMovie from App Store not compatible with ElCapitan

I have a computer that will not run latest OS (Mac Pro Tower, 5,1). I have it running El Capitan, as it is compatible with all other software I use anyway.

I wanted to install iMovie which is a free app on the App store, but received the following error message:

iMovie can’t be installed on “Mac HD” because OS X version 10.13.6 or later is required.

When I looked this up I found an article (https://discussions.apple.com/thread/8299452) that claims I can download the older versions at the App store. This no longer seems to be the case.

Is there another solution to finding copies of iMovie from Apple which are compatible with El Capitan?

MacTVMan