Venu 4 - Heirloom watchface - how can I select heart rate to be shown?

I'd like to see my heart rate on the official Heirloom watchface, but I can't find it in the list. (There are metrics like "cycling vo2max" and such, but no heart rate, I guess it would be much more interesting to see, since the former does not really change a lot during a day.)
Is it possible to select it somehow, is it just a bug, or am I missing something?

Venu 4 - 41mm, FW 17.39