COMING SOON!
Although Challenges are technically on-demand, they are not "activities" but, rather, goal-oriented tasks where players aim to achieve targets like moving time, distance, or elevation gain over an extended period.
Complete challenges, win races, and take part in events to earn coins through gameplay.
From either the Home Screen, choose a Challenge. You can also find Challenges under My Stuff.
For example, you may see this in Challenges: