Sort of. If you’re receiving a notification from a remote server on iOS or standard android, they go through Apple or googles servers. That said, some apps rather than sending your device the actual notification (where this vulnerability comes from) will instead send a type of invisible notification that basically tells the app to check for a new message or whatever and then will display a local notification so the actual message stays on device and inside of the hosting services servers (like a self host.)
I didn’t know that. Hmm, sounds like it’s decently likely this is a bit overblown then. I mean, I suppose there are a lot of lazy companies out there that will skip this, but that severely limits the functionality in a way that it’s going to force the secure method.