Check out these threads –
Xert Data Fields on my Garmin - Support - Xert Community Forum (xertonline.com)
Hints for training outside - Support - Xert Community Forum (xertonline.com)
TL;DR Many Xerters ride outdoors by RPE or HR with lower intensity miles in mind. Others follow the focus method to meet their goal for the day. Some live in areas conducive to performing workouts on the road as long as you are selective about which workout and realize you don’t need to follow it exactly to achieve the intended results.