Right out of the box, the Garmin Enduro reports overly generous total elevation gain numbers. I prefer my GPS watch to be accurate not generous. Before the Enduro I had been using the Fenix 3 HR for a number of years and its accuracy has been time-tested against so many ultra trail races I’ve ever been in. So I have a solid reference to compare the Enduro with. With that said, I suggest making the following changes:
Long Press MENU button | Settings | System | Data Recording | Every Second
Long Press MENU button | Settings | Sensor & Accessories | Altimeter | Auto Cal. | During Activity: OFF | Not During Activity: OFF
Long Press MENU button | Settings | Sensor & Accessories | Barometer | Watch Mode | Barometer (Default: Auto). I’ve found Auto jacks up elevation gain a lot and until a future firmware addresses this problem, the only way is to force Watch Mode to Barometer (more info from Garmin)
Before starting an activity, calibrate your Altimeter using DEM where DEM is supported. Otherwise use GPS (less accurate)