How do you get an iMovie older version you need for an older OS X?

After hours of search, this actually answered and solved the issue:

gaetanotuf

User level:

Level 2

(283 points)

Jun 12, 2020 2:48 AM in response to omega7785

Yes there is a way, you have to download and install iMovie using a device that supports the actual version of iMovie, you can also use an iPhone or an iPad, the most important is that you will use the same Apple ID used for your Mac.

Once you have done that you will find that in High Sierra > App Store > Purchased App you will have the icon of iMovie and being able to download the most compatible version for High Sierra, that is archived and available only for customers that they have already purchased the app.