You should be able to kind of do both through android settings

Settings -> Apps -> YourApp -> Mobile data usage -> Allow Network access and Mobile Data

For VPN you’ll need to add a VPN and then Settings -> Network and Internet -> VPN -> YourVPN -> Always on VPN and Block Connections without VPN. This blocks all apps. There is 2 issues with this though, Blocking connections will block split tunneling connections set up through VPNs and also potentially this depending on the apps you’re using https://mullvad.net/en/blog/dns-traffic-can-leak-outside-the-vpn-tunnel-on-android

https://www.businessinsider.com/mark-zuckerberg-facebook-execs-decrypt-rival-apps-usage-snap-youtube-2024-3

This is a ‘man-in-the-middle approach,’" the email said.

Yep, this article has more details about it

https://github.com/mozilla-mobile/fenix/issues/417 it was requested back in 2019 for Firefox and is listed as a known issue on Mull https://divestos.org/pages/broken#mull it seems like Mozilla has no interest in implementing it. If you’re rooted you should be able to access the file though

I’m pretty sure Element stays active in the background, it may have asked you to turn off battery optimisation and have a silent notification always active. This decreases battery life which is why most apps don’t do this but it allows the app to constantly ping the server to check for new messages and is one way around using FCM.

Fair email uses https://en.m.wikipedia.org/wiki/IMAP_IDLE instead of FCM, I’m no expert and this is just my guess but it seems to also need the app to run in the background for this to work.

Silence is SMS and MMS only and so doesn’t use internet and so has no need for FCM or any alternative anyway

For android, Google uses Firebase Cloud Messaging, basically a server that pings the phone when a notification for an app is available, which wakes the app up to receive the notification. There are alternatives but they need to be adopted by app devs for them to work.

For people running a degoogled android, they’ll notice most apps won’t receive any notifications until they open the apps since most apps rely on Google Play Services to receive a ping from FCM.

I don’t have any google play services so most of my apps don’t give me push notifications but I do have WhatsApp installed and that still receives notifications, they’re sometimes delayed by a few minutes which makes me think Meta have their own implementation/alternative to FCM but I’m not sure.

For Signal, their servers tell Googles FCM servers that you have notifications waiting on Signals servers and to wake up your Signal app so it can communicate with Signals servers to receive your messages.

WhatsApp and Signal claim/have end-end encryption on their messages but that shouldn’t matter when specifically looking at Googles FCM servers so, at most it would be meta data that could be obtained from the FCM servers.

https://jami.net/unifiedpush/ has a pretty basic explanation of push notifications on android and also showcases an alternative to FCM https://unifiedpush.org/ which has a nice little diagram about push notifications on android. Unfortunately, Unifiedpush is not widely adopted by many applications.

So there are ways to avoid Googles FCM servers on android using Unifiedpush or always having the application on in the background but for the most part FCM is used.