Hi Darren,
There are a number of flaws in what you are saying and doing. What Yordie says is correct. However, I want to address a few things you said and try to help point you in the right direction.
While exporting a KML 3D path from Litchi and loading that into Google Earth Pro will work, a much easier way would be to use āVirtual Litchi Missionā which automates those steps while providing even more functionality. If you are not familiar with Virtual Litchi Mission, do some searches. You will find a lot of information about it.
While it may be possible that elevation data for some areas of the globe is not available, it is unlikely, and I have never come across any.
This is because you do not have the āTerrainā checkbox checked in Google Earth Pro. I can see from the snapshot you included the box is not checked. As a result, Google Earth Pro is showing satellite imagery without any elevation data. You need to check the āTerrainā checkbox as shown here:

If you tried to fly a mission with a waypoint set to -200, your drone would try to descend below ground (but would probably be prevented from doing so due to its landing protection).
Litchi doesnāt have elevation data. Litchi uses Googleās elevation data.
To summarize:
- All heights are relative to the take-off height unless you have the āAbove Groundā option checked. If you are flying in a relatively flat area, simplify things for yourself and leave that unchecked.
- Litchi uses the same elevation data that is used in Google Earth Pro ā Googleās elevation data.
- If you want Google Earth Pro to show proper terrain heights, check the āTerrainā checkbox.
- Use Virtual Litchi Mission to help plan your flights.