I am totally new in mobile app development and consequently very confused about how to get going (independent from how much I have read Google Drive API documentation over and over again.)
The way I would like to implement my (initially "android") mobile app (which I will develop by using ionic):
Question 1) Does this approach make sense? I ideally would like to eliminate the work for back-end development. Or would you suggest another approach to do the same thing (with or without Google Drive)?
Question 2) The authorization process looks quite confusing to me as it is explained in Google's documentation. I could not find relevant information only addressing the scenario I have in my use case. Requirements: The mobile apps can fetch the corresponding file (or the content of it) and process it to show to the end user, but mobile apps (or any other client) may not update/edit/delete the file, cannot add a new file either. The only purpose of using the Google Drive will be to enable the mobile app fetching the data that will be shown to the user. How can this problem be solved by using Google's OAuth framework? A step by step action plan would really be appreciated.
You are also welcome to share your view if I should instead consider using Firebase for my problem, which I guess will be more costly.
Based on discussing the requirements with you, I would recommend against trying to do this with Google Drive API.
There are no tutorials out there for Ionic 4 + Google Drive API, and only a few for older versions. It will be an uphill struggle to create a solution that isn't going to scale well.
Instead you should start looking into using Firebase.
There are lots of tutorials which show you the basics: setting up a login system, and reading some data from the database.
The free limits are quite generous.
You can implement caching into your app so that you store a copy of the data on the device, and only refresh it either weekly, or more advanced, put a second table in that records the last updated date for the main table.
Firebase charges by reads so if you can set it up so that you only read one record (last updated) instead of downloading the whole database every time, then you can stretch your free tier a lot further.
If you do outgrow the free tier and the app is not generating enough to cover the costs then you have the option of investing time instead of money. There are guides in the docs about exporting the users and they provide tools so that the passwords can be put into another system without requiring the users to reset their passwords. The database can be similarly exported.