What special equipment and accessories do you need for Apple Fitness Plus? When shopping for workout gear, what should beginners know? The Apple Fitness Store lists a lot of gear but should I look at other online stores as well?

I just got my iPhone 14 Pro and was looking forward to using the fitness app but the rings just stay entirely blank. I even have other apps linked (Fitbod and Strava) and workouts from those apps appear in Fitness but the rings stay entirely dark. Is it possible to use the Fitness app...