How to sync iPhone HEIC / HEIF photos to MacBook Photos v1.5 (El Capitan)

My iPhone (iOS 12.3.1) takes pictures in HEIC / HEIF format. I have an older Macbook (13" mid-2009) with MacOS El Capitan, which includes Photos v1.5. When my iPhone photos get synced via iCloud to the Macbook, the thumbnails show up fine, but when I click on the photo, a large grey exclamation mark is shown. What settings should I change to ensure they're also viewable in El Capitan Photos 1.5? Please note that I'm not looking for another tool to run manually prior to each sync, as suggested in the "Duplication Question" suggestion. I'm just looking for a set of configuration settings that others are using successfully, to take pictures on the iPhone using HEIC / HEIF, and view *automatically* (i.e. without using another tool manually) on my Macbook El Capitan.