how do I turn on the Heart rate option so it is visible during workout

OK. Those should all already include heart rate by default. Within that multiple view, if you hit the Edit button, you can also reposition them by grabbing and moving the handle on the right. But you said it is all greyed out as well. That is not normal at all with those workouts.

Is heart rate still recorded during your workouts? If problems continue, try unpairing and repairing your watch.

Unpair and erase your Apple Watch - Apple Support

Could it be the case if there are already five metrics in the Metrics section? In that case you can’t add additional metrics without first deleting one of the metrics that’s already included.

Which workout is it? I am not sure from the picture :)

Is the Heart Rate app showing your current beats just fine ? Is the power saving mode disabled during workouts?

Awesome - great to hear.