@Martin-Wilcke do you intend to drive all that TET sections in one ride? That will last 2-3 Months...
My longest rides to Morocco and round Italy lasts each 5 Weeks. I splitted the routes in parts - one for each rinding day.
In your case, I would import the gpx to get all <wpt> as Point of Interest. Then I would import the gpx again to get the tracks. If all the sections are in one gpx, you will get one object (Route-Track) for each section.
Then open one of the Route-Tracks and select in the options "rework the track" - this will convert it to a route. Now in this Route, you can go to Waypoints and activate in Tab "Bibliothek" your before imported POI list. This will populate all POIs in the route (you will see it only in a lower zoom level).
If you then open MRA Navigation App, open one of these routes to navigate, then you will also see all that POI. Before, you need to have activated synchronisation between MRA-Navigation with MRA-Roueplanner.
