It is not possible to sync data from Apple Watch directly to Garmin Connect, but it is possible to transfer data by manually uploading the files or by using the RunGap app. Needless to say I have finally subscribed to a year of service to get it sync automatically using RunGap. Doing it manually was just too much hassle. I use now regularly my Apple Fitness+ workout classes with Apple Watch and I am cycling outdoors with my Garmin computer.

This article explains how to sync data from Apple Watch to Garmin Connect, including using HealthFit to export a .FIT file, setting up RunGap to export to Garmin Connect, and using the auto-sharing functionality. Unfortunately data such as steps, floors, sleep, and all-day heart rate data cannot be synced to Garmin Connect. But at least now I have got all my Apple Fitness+ workout classes synced with my outdoor cycling data in Garmin Connect account and shared across to Strava as well automatically so it is worth the couple of dollars as month expense.