I believe this is the same problem as reported on the 945 here: https://forums.garmin.com/sports-fitness/running-multisport/f/forerunner-945-lte/289173/disable-lap-button-during-workouts.
Garmin FR 745, firmware 12.10. In "Run Settings", the "Lap Key" is set to "off."
Expected behavior: during a running workout (using a pre-created workout), hitting the "back" button should do nothing
Actual behavior: during such a workout, the "back" button skips to the next step in the workout
I assume this is a fairly trivial fix. Can we please prioritize it? It's really driving me to consider leaving the Garmin ecosystem.