My Android app targets SDK 28 and connects to Google Fit to upload data and read some other data. The app uses the HistoryAPI to read com.google.step_count.delta data.
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Looks like the documentation was updated: https://developer.android.com/about/versions/10/privacy/changes#physical-activity-recognition
I was able to solve this by only using the API 28 permission in the manifest (com.google.android.gms.permission.ACTIVITY_RECOGNITION).
If the app was installed on a device running Android 10 (API 29), the system appears to correctly auto grant the permission android.permission.ACTIVITY_RECOGNITION.
Because the user can change this in settings (Settings > Apps & Notifications > Permission Manager > Physical Activity > specified app > deny), I was able to check the android.permission.ACTIVITY_RECOGNITION permission if the app was installed on a device running Android 10 (API 29).