Full disclosure, I’m one of the creators but you might want to check out https://feathersjs.com/. We even had an article back in the day about how you can use Feathers as an alternative to Firebase: https://blog.feathersjs.com/using-feathersjs-as-an-open-source-alternative-to-firebase-b5d93c200cee.
Things have evolved quite a bit since then and you can do everything Firebase does but in an open source way. 😁
Thanks for writing such a great article HomeAutomation!