It depends on your challenge! Some challenges offer a “Report an Activity” option accessible via the “Move” button. If you have this option, you can manually enter the duration of your indoor activity and earn points accordingly, without GPS.
If this option doesn’t appear in your app, then unfortunately this type of activity can’t be tracked. The app relies on GPS to record activities, and indoor facilities don’t have GPS 😅
Generally speaking, if an activity doesn’t appear in the list, it means it’s not available in your challenge 🙂