it looks like Gamin has added automatic mode tracking for backcountry skiing in ver 17.26. Unfortunately it's quite buggy. It's supposed to detect if you're ascending, descending or transitioning, but it doesn't work properly. Here's a recent example:
- Between 0.89 and 1.56 miles both the map and the elevation chart show a "descent", but actually I was still ascending
- Between 3.78 and 4.03 miles the map shows an ascent, which is correct, but the elevation chart shows a "transition", which is wrong.
Activity details here: https://connect.garmin.com/modern/activity/13043356808
Another user has reported the same problem: https://forums.garmin.com/sports-fitness/running-multisport/f/forerunner-955-series/335148/ski-mode---no-auto-pause-setting/1703387#1703387