Using ROUVY and Zwift. They sync to my Garmin connect but do not appear in the count for the challenges.
If you actually have a Garmin device, you can export the activity as a tcx file in Garmin, edit it and add the “creator” section at the end (before the </activity> tag). Simply copy this from another activity that was recorded with the Garmin device. Then GC sees that it was a Garmin device and recognizes time/km/... also for challenges. Just tested with an activity from ROUVY. Tedious, but it works. Of course, you then delete the original unit. You may have to adjust the date/time if you rode in a different time zone in ROUVY. This seems to be falsified by export/import.