Update: You should now be able to resolve this issue by updating your iOS to version 14.2.
Due to an issue with iOS 14 and watchOS 7 outlined here, if you've recorded an outdoor activity with the Apple Workout app, but no GPS data was recorded, the activity may fail to sync to Strava or the imported activity will appear as an "indoor activity". You can confirm whether your activities from the Workout app have GPS data using either of these options:
- Health > Browse > Activity > Workouts > Show All Workout Routes
- Fitness app > tap the Workout that imported without a route. Check whether the route is displayed below the map.
If you're not seeing a route in the Health/Workout app, please review the article Apple has posted to resolve the issue: https://support.apple.com/en-us/HT211865