We experiences same issue. It should be fixed now, we can see all apps again.

According to documentation SensorKit places a 24-hour holding period on newly recorded data before an app can access it. This gives the user an opportunity to delete any data they don’t want to share with the app. Did you wait for 24 hours at least? Most important part is: A fetch request doesn’t return any results if its time range overlaps this holding period. Are you sure your time range doesn't overlap the holding period?

Yes, it allows passive collection. In fact your app doesn't need to run in background at all, it can be killed. As stated in documentation system keeps 7 days of data for you. Data older than 7 days are deleted. Also SensorKit places a 24-hour holding period on newly recorded data before an app can access it. This gives the user an opportunity to delete any data they don’t want to share with the app.