It is not possible to import Google Earth files with kml or kmz extensions. What would be the solution to plan flights?
The new Litchi Mission Hub (v2) does not yet have the KMZ/KML import ability. However, the developers are working on it so it will be available at a future date.
Most people use the Mission Hub to plan their flights. If your workflow requires that you import a file from Google Earth, you can still import those files using the old (v1) Mission Hub.