Thank you for your comment. Since I deactivated Google Play services, I don't get notifications on many apps. I didn't know there were alternatives. Unfortunately, the app server must be compatible, but if I can have it at least for Telegram with this fork, it would be a good start. I'll take time to compare the different alternatives and see if other push servers are compatible with more apps.

For what I understand, there are self hosted push servers, like NextPush that works on Nextcloud, and some that provide you a server, liked ntfy. For the latter, you have to check the privacy policy to see if it's better than the default Google firebase server.