You may use a treadmill for running and walking games that accept photo submissions for verification. Just upload a photo of your treadmill’s dashboard with pace and duration showing after your workout.
Many games require syncing a tracker, however, so be sure to check the verification type before joining.
For games that require syncing a fitness tracker, walks and runs on treadmills MAY still work. You’ll need to check that you’re using a supported tracker AND that it has an indoor run or treadmill setting. Devices that track outdoor runs only will not work on a treadmill.
In order to track a treadmill run, your device MUST be able to capture distance, duration, pace, and heart rate data for the activity. These are generally wearable trackers like Apple Watch, Fitbit, and Garmin.
Workouts on ellipticals and other gym equipment will not count for running or walking games.