Only heart rate on map screen while following a course/navigating.

How can I change what screens are shown while navigating, and what they show?

You can customize the map screen using real time settings within the Garmin Connect Mobile app. Make sure the watch is paired and connected to the Garmin app. Open the Garmin app on your smartphone and select more> Garmin devices> Select your watch> Activities. Select the activity profile you want to edit. Data screens> Map. There you can select the layout and edit the fields. Back all the way out and sync your watch to apply the changes. 

The bottom black “next navigation point” box cannot be removed.

This is why I have been begging Garmin for a year (fenix8)

Exactly. I would like to remove that one such that I can see the hr with the single data field layout.

And also I think the new solution where you lose the ETA and distance to finish data screens is not good.

How can we make you listen to our suggestions!

Do you have threads on the Fenix 8 forum discussing this?

Help me suggest the change: https://www.garmin.com/en-US/forms/ideas/

Fenix 8 navigation bug :Disable Bottom Black field not possible - fēnix 8 Series - Wearables - Garmin Forums

You can just add them  I don't see the problem