Date and Time, Activity Info, Biometrics, Training Status, System, Environment, Garmin Weather, Sun and Moon, Twilight & Golden Hour, Plugins, and Custom. What you see depends on your watch.
What you may see next to a field
In the list
What it means
[PRO]
This field needs PRO. You can try it for an hour, then it shows PRO instead of its value. See Free vs PRO
Not Installed
This field needs a plugin app that isn't on your watch yet. See Plugins
After choosing a field
Back in the menu of the field, you can change more:
Data Options: format, units and how often it updates. See Refresh Time
Label: an icon, your own text, or even a second data field
Color Overrides: a text and label color for this field only
Offsets: move the data or label by a number of pixels
Good to know
Progress bars and rings only list data that can show progress.
To remove a field, choose Nothing (remove) in the Custom category.