I realize this isn’t your point but I feel the need to point out that skinheads are not nazis - it is unfortunately a very well working project of cultural appropriation by the racists.
In the scene racist skinheads are mostly referred to as boneheads, a term which I think makes much more sense.
Not all notifications go through FCM but all push notifications do as far as I’m aware - which is what the previous comment and the post title are talking about.
It is, in fact, worrying for privacy implications on the one hand and a real monopolizing factor on the other since if you wish to deliver an app which needs to implement such notifications you’re using Google’s service or constantly drain the user’s battery.
There’s UnifiedPush which tries to provide an open alternative but so far unfortunately still sees very little adoption.