I'm by no means an expert in this area but here's a brief rundown of my understanding.
To start with, I would say that all of these measurements are approximations. None of them take variations in elevation into account (obviously). My understanding is that, for very sensitive measurements, other methods are used.
That said, you can get pretty good approximations of the great-circle distance between two points on the earth's surface using the geometry engine. If you have two points with a longitude, latitude, and altitude, the geometry engine won't help (it appears to ignore the altitude), but you have some other options.
One of them is to take the average of the altitudes of the two points and find the great-circle distance between the two new points. In practice this gives reasonably good results. The farther the distance between the two points, the greater the error. I would say this is acceptable for most normal use cases.
Another is to convert from a long, lat, z coordinate system into a 3 dimensional cartesian coordinate system (ECEF is a commonly used one). Once you have two points in ECEF, you can use the distance formula to calculate the straight-line distance between the two points:
let d = Math.sqrt(Math.pow(x1-x2, 2) + Math.pow(y1-y2, 2) + Math.pow(z1-z2, 2))
Here's a stackoverflow question and answer that provides some code that may be helpful if you want to implement either of these options: geometry - Taking altitude into account when calculating geodesic distance - Stack Overflow
