As I use #Conversations #XMPP client to chat with my family I configured it to be also an #UnifiedPush distributor.
This reuses the already existing XMPP connection to also serve other android apps for push messages.
On server side I used #ejabberd community module mod_unified_push.

It works nicely.
When I update event in nextcloud, DAVx⁵ gets notified and update is immediately synced to phone.
When I get new notification on Mastodon, Tusky is notified and notification shows on phone.

I hope more apps are going to support this in near feature.