heading, GPS heading and compass heading.

I do not know for sure. Typically, the way this works is that the reported heading (the first one here) is based on the electronic compass unless you are moving fast enough for the GPS-derived heading to be meaningful. I don't recall the threshold speed - maybe 2 miles an hour (which is a strolling pace).

I would not expect GPS heading to be shown if you are moving too slowly. If it IS shown, it would be stale (for example last GPS heading when you were moving fast enough.)

To further muddy the waters, I don't know which of these take into account your preference for true vs. magnetic.

Thank you, twolpert.

This displays your direction based on the compass. It’s influenced by the device's internal magnetic compass, making it useful when GPS signals are weak or unavailable. Keep in mind that it’s prone to magnetic interference. This shows your direction based solely on GPS data. It calculates your heading based on your position changes over time and is generally accurate at higher speeds or when moving in a straight line, as it relies entirely on satellite data.