What all do I need to learn(backend) as a frontend dev to deploy my first app?

So I'm trying to make a sort of a simple time management app. I'm a frontend developer, been working for less than a year. I've worked on Angular, React, Ionic. So I'm sure that I'll be making a PWA and putting it on the iOS and Android app stores. That's the front-end part.

Now I need help figuring out the backend. I have no experience and don't know Go or Python. I have some experience with Firebase.

So in the beginning at least, the basic features I want to implement are,

  • Login via Google/apple.

  • Backup the settings and data of the user.

  • Run Notifications

So my questions are,

  1. What services(Kubernetes/ Docker/ Amazon S3/ Firebase etc) would I have to use and learn?
  2. What languages (Python/ Node.Js/ Golang) would I need to learn? (Other than for front end, there I'll be using ionic + Angular)
  3. How do you decide what tasks will be handled by Backend and what will be handled by the frontend, in case of stuff that can be done by both?
  4. Any other info that I should look into/ think about and anything else I should learn?

Thank you so much!