FYI for the other commenters, UnifiedPush can work thru the Prosody mod_unified_push or any server with a up where Conversations (& its forks like Cheogram, Monocles, Blabber) can be a distributor. This has the added bonus of coming with an awesome decentralized XMPP chat server getting to reuse a single connection & single app to server instead of separate ones. Conversations is the most efficient chat client on Android in terms of resources (battery, network, RAM) so might as well keep it lightweight—which you are probably trying to get push notifications from the likes of Signal or Element, but what is the point when you have an efficient XMPP server for your chat needs?

However, I think UnifiedPush might be a bit flawed—as if the startup that created ntfy is pushing others to try to adopt their standard instead of getting folks on board with the older & capable MQTT (which also can be ran thru mod_mqtt on your XMPP server). I am not yet sure if this is a tinfoil take or not.