If you are to make a mobile store app, would you use a CMS for managing data or build your own software?

Hello, I'm learning flutter for building mobile apps and want to make my hobby project as a store (for training purposes) .

But controlling data from Firebase directly is not best practice. I don't know if there is some sort of CMS like solutions but for mobile apps only, or Should I implement a website and provide my own APIs to use in mobile apps ?

Also (out of curiosity) , how do businesses that make their mobile apps , manage their data?