Since my last post about it, the method to upload via Garmin Connect has stopped working. It relied on using the old version of the Garmin website, which has been taken down. I now use GPSBabel with the front end gpsbabelfe (listed as gpsbabel-gui), both available on the Linux Mint repos. Using the input options: snwhite=0,get_posn=0,power_off=0,erase_t=0,resettime=0 and output options: course=0 Works well and can be uploaded straight into Strava.
Interesting and useful things that I have found out and want to share.