I dont have much info on this feature but it would appear push notifcations are only supported for SFBO users at the moment when using Android. As if you have an O365 tenant the PNS will say "supported". PNS only used to be required for Windows Phone and Apple iOS. It was my understanding that the Android architecture didnt require a clearing house for push notifications so im curious as to why this setting has been added into Android and underhood how it will function compared to WP or Apple iOS which both utilize the Microsoft O365 clearing house.