Elevation not updating during Walk activity

For devices that have barometer it's used by default. For devices that don't have Garmin automatically calculates the elevation, but not from the GPS elevation data because it's much less precise than the 2d coordinates. It uses the same data that your watch uses to calibrate it's elevation, by knowing the estimated elevation based on your coordinates. 

If you look in the Garmin connect website then looking at your activity, on the right side it'll show you which elevation mode is displayed. And if you want you can disable the default.

However you might kind of found a bug, 'cause if you set your watch to treat the change in ambient air pressure as change in the barometer then IMHO it should treat your activity the same way as fir devices that don't have barometer.

But the easiest fix is to set it to either auto or elevation, then the pressure changes during activity will be used as change in elevation

Thank you, enabling elevation corrections did the trick. I agree, however, that using DEM data should be the default when the altimeter is disabled. BTW, I thought that the watch is doing some sort of a sensor fusion from barometer, GPS and DEM data (Kalman or something like this), but it looks like this is actually much simpler.

No, I don't think it's simple. About 2 years ago there was a firmware version after which many users started to complain that the Auto setting works worse than before. The rumor was that Garmin probably used some algorithm that worked pretty well but some other company owned it and Garmin didn't want to pay so they had to change the algorithm, that's what made the auto setting so bad. Apparently it's not an easy task to differentiate barometric (aka weather) changes from elevation changes

flocsy🤠 Concerning the barometer only option, from the 965 manual: "... the Barometer Only option when your activity does not involve changes in altitude."

www8.garmin.com/.../GUID-2DF9C415-2A35-48CE-B20B-013DAA3358A5.html

Indeed but based on the graph from your girlfriend's activity there was real elevation change

I interpret the Garmin's manual as "if set to barometer only, elevation is not tracked".

Exactly. That's why it's flat