Is it possible to export data stored related to activities?
There's at least a couple of ways:
1) Make a GDPR request to Garmin: https://www.garmin.com/en-US/account/datamanagement/
2) Use this python script (note the disclaimer): https://github.com/pe-st/garmin-connect-export
3) Sync your Garmin Connect account with https://www.runalyze.com and use their option to backup your data: ideas.runalyze.com/.../bulk-gpx-export-of-activities-as-csv-file
