@Martin-Wilcke Thank you for your help. I am interested in further testing
Your number 3 test works, that all VIA points are now being shown. But the whole route is gone. The route is now point to point shown.

Unfortunately, the Montana route planer does not show the VIA points in a list as your Zumo does. This is a sutpid Garmin software decision, as the GPSMap 276Cx could do this and was based on Montana software.. the only option, where is does show VIA points like Zumo in a list, if I do transfer a route from Basecamp with "Direct Navigation". Thats the only case, where this works. You can find such example route here: clickme (This means only straight lines, no routing)
This is can example, what I mean. It only works with my uploaded direct Route from Basecamp. Your "MRA Route Version 3", despide being direct, does not show its points, so it's apprently not detected as direct route?

@Hans-van-de-Ven-MR-MRA Great, many thanks. Do you want to open for that a support ticket?