I have been using the Garmin connect app on my phone for a few years and have it set to statute UK.
Both the web site and the phone app display weight in stones and pounds and let me enter values as such.
Recently my wife started using Garmin connect and I checked every setting on both the app and the website and her weight is displayed in pounds only. I cannot find any way to change it to stones and pounds.
There must be a setting somewhere as my account works but my wifes does not.