Does anyone know how to do Push Notifications without Onesignal and Cloud Messaging?

Hello, I am looking for a tutorial or extension that allows me to send push notifications to users without the need for OneSignal or Cloud Messaging (I doubt there is)

Yes i have one idea.
You can use notification component and use background task extension.
And use firebase.
In firebase when you change tag value than the background task extension also running firebase and notification component in the background .
It will show notification
But for this idea i think you need much much hard work

It seems a good idea. Could you explain your idea with higher detail, please?

Ok i will check it first