There are reports/Youtube videos that you can use the Apple Watch for running to capture both your step/stride and heart rate.
But with both the Zwift and Companion apps on iOS – it never has worked or only works momentarily before stopping to work. It led me to get a HR monitor strap so I can ride on the indoor trainer.
However, now that I signed up for the Academy Tri – I need to get the AW S4 working if possible so I can run on the treadmill (or possibly outside).
I’ve reboot both the phone and AW and attempted to fix the connection between device and AW.
I am running iOS 13.2.2 on iPhone 7 and it seems I am about to update to 13.2.3 (now).
I am running watchOS 6.1 on S4.
I am happy to help/troubleshoot – I do mobile software on iOS – and happy to produce any logs if you find helpful.