I got an invitation to try out the new "modern" Garmin Connect today, and saw the following:
"Our Garmin Express is the new way to transfer data to and from Garmin Connect. There is no 'Upload' button in Modern."
I am a linux user. I plug my watch in to my computer where it is mounted as a USB mass storage device. I copy the fit files off, and upload them to Garmin Connect using the "upload" button. Garmin Express is only available for Windows/Mac. Can you please keep the "upload" button in the new Garmin Connect?