Now why am I not surprised, things don't do in Garmin software, what they say and should :D

Thanks anyhow, I will test the Basecamp-method, though I try to avoid Basecamp. (It lacks the detail for offroad riding apparently. At least as far as I have seen.)

Also it"s enough to sturggle with ...

Thanks, great information source. Very helpful opposed to the alleged support/documentation given by Garmin in any shape or form ;)

I am still not clear about how to solve the following seemingly simple task:
If I have some tracks (1 to X) I want to connect for a longer Route (which I can save ...

I. COPYING a GPX file from a PC via USB (including Tracks & Waypoints)
Copy GPX-file to
"This PC\zūmo XT\Internal Storage\GPX"

Apps > Tracks (UI GETS VERY VERY SLOW/LAGGY)
Tracks visible, Explore sync needed-symbol

Under Where to? > Explore >

All
Tracks not listed (which are visible ...