After receiving an email from Amazon regarding Sidewalk some weeks ago, I immediately followed their instructions for disabling the feature and that was that. However, I checked today and where there was previously "Amazon Sidewalk" listed in my settings it had vanished. Gone. So I updated the app (Android) to the lastest version and magically "Amazon Sidewalk" has reappeared in settings. Happily, it was still disabled as I had originally set it.
Very strange.
