I have a USB (C) to USB (A) connector to connect my Garmin Mini USB (B) lead to my phone.IMG_20231031_195702573sml.jpg I can transfer routes from MyRoute-App to my old garmin devices by downloading the route to the phone connecting the phone to the device and transfering the GPX file directly.
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I'm sure that something similar could be sorted with a chromebook. Alternatively if the chromebook has a micro SD slot copy the file to the micro sd card pop it in the Nav 6 and copy it to the unit.