Well, not every support has enough knowledge and can try them all.
We were already in the Black Forest and had loaded the wrong GPX file on the Garmin, downloaded it again with the Samsung and transferred it via cable to the external map in the Garmin :-)

It should also work under Linux, the navigation system switches to "USB memory stick mode" when a USB connection is established.
This works fine with my Android mobile phone. The decision for this model was to be able to copy GPX files to the Garmin via mobile phone and USB cable.

For me, the data transfer with Ubuntu 17.10 works without any problems. The Garmin logs on as expected as normal drives (device + SD card) that can be read and written.