Comment by tranq_cassowary

Communication between apps using IPC happens on mutual consent and is explicit. You can't just throw data to Play Services and expect it to accept it and process it well, that's not how it works. Communication via IPC is always very intentional and specific, so it will be very structured data for specific purposes, not just a dump of all your data. Firebase Cloud Messaging (FCM) is a push messaging service, it doesn't need to be used to send the actual notification. It's perfectly possible to just use FCM to wake the device and then handle notifications by yourself as app. The way FCM can be used is much different from Apple's system. Apple forces you to use their services for notifications while Google allows you to use FCM just for waking your device. It's also possible for apps to not use FCM at all and to just use WebSockets or UnifiedPush.

If you just grant Google Maps location permission and don't give it to Play Services and keep your sandboxed google play settings to the default, the location requests are rerouted through the GrapheneOS servers. If you want to use network location to get quicker location locks and location indoors, you can also use GrapheneOS network location, so you don't need to use the Google implementation for that.

And, even if you would decide to use Google directly for the location, you can perfectly avoid giving permanent location access. You can hand it over only once or only when the app is in use. So Google doesn't know everywhere your phone goes, at all.