Right UP, I see your problem.
Like most satnavs when you put a sequence of route points into it, it will calculate a route to follow the roads in between those points. Google earth does not do this for you. IT is not intended to be used for creating a route. For that you need some route planning software.
What you have loaded in, is a GPX file that just contains the points. Without anythingt o describe how to link the points together, most software will create what is called a 'direct' route. ie it will join up the dots with straight lines. When I loaded it into Basecamp, it looked like this:
So if you try to fly your KML file in Google earth Pro, it would take you literally through the mountains. Following the straight lines, straight into one side of a hill and emerge nursing a nasty headache at the other side. No. That is no good. What GEP needs is the route itself, not just the points that represent the individual route points.
If you have the Basecamp maps of your area, then get Basecamp to create the route from your points and export that as a new KML file. Load that into Google Earth.
If you don't have the Basecamp maps, then it needs different solution that does the same job of creating a route along roads and creating a new KML file that plots the twisty windy route along roads.
One way that is nice and convenient is to use MyRouteApps. But other methods also exist - and the software that you use already may have the facility to create a route and export it to a new kml file - I don't know.
MyRouteApp wll allows you to set up a free account.
Load in your direct route KML file. MRA will immediately create a twisty-turny route along roads - like the screen shot below - although it seems to have joined the end back to the beginning. I've not bothered to find out why.
Don't do anything with it except save it again, choosing the KML file option. It will save it with exactly the same name but with a number in brackets added.
Then load that new kml file into Google Earth Pro.
When I tried it, the route showed up as a very fine white line. (So it almost didn't show up). It will still fly the route when you click the 'Play Tour' button
But if you want to make the route line easier to see, before clicking on the 'Play Tour' button, you right click on the track that you have selected to get the pop up menu, and then select properties, you can select the colour, width and opacity of the track that is displayed. I'm on a PC - you will have to translate that last instruction to Mac-speak if you use a Mac.
If you need more detail, I will happily provide it.
I've attached the twisty curvy kml file below so that you can use it to try the google earth flying bit without doing the part with software like MyRouteApp or Basecamp.
