Need at least the camera, if not that plus a microphone and speakers, not the lock or bell.
Libre Software (Obviously) + End-to-End Encryption
Small and easy to hide, so the camera isn’t stolen, attacked or bypassed.
I use Eufy doorbells, locks, and cameras. I realize they are a Chinese company, but that is almost unavoidable until the US gets back to actually manufacturing tech.
The reason I like Eufy is the local storage and no required subscription fees.
Harder for China than the US to attack in the US.
Reolink has a local encrypted video doorbell.
You don’t need a doorbell camera, get a regular camera instead.
You need an app which will receive events from a doorbell via a server to receive data to interface with the app. Both of those things need to be owned and operated by someone to be approved for use on the app store. That’s why a custom open source of doorbell as you envision it doesn’t exist and never will.
I agree mostly except the app. Don’t pretent Home Assistant doesn’t have an app.