Garmin Connect does not do live the way Strava does, unfortunately. You can just view your heart rate from the My Day screen. Or, if you start a LiveTrack session, with yourself as a recipient, you can then open the link in the phone's web browser. You'll see a map with some metrics.
In the past I have always used Wahoo Fitness app for that functionality when I wanted it. When finished it was very easy to export/share the .Fit file to be imported into Garmin/Strava. I haven't used it in a couple years however, might be different by now.
I used it mainly for indoor bike training - allowed you to connect power meter and HR strap
