What does "limited functionality with courses feature" mean for Forerunner devices?

On the Explore App compatibility page (https://support.garmin.com/en-US/?faq=o2VcUgraJX4twZzO1ME7z9) under the Forerunner Watches section it says: "NOTE: Forerunner watches will have limited functionality with the courses feature in conjunction with the Garmin Explore app."

What exactly does that mean?

I had created a course in Garmin Connect and synced it to my Forerunner 955 and then was trying to get that course to sync from the watch to the Explore app but it does not show up (activities are syncing correctly). I ultimately went to the Connect website, found the course there, downloaded the gpx, went to the Explore website, and then uploaded the gpx. Not sure if this is one of the limitations of forerunner or if this also doesn't work with Fenix watches.