So where do you think these files that are used are stored?
Every app that reads and writes files shows your standard file picker that lets you load and save files that can then be shared across applications. This has been the case for years.
If you start to really 'obsess about the details' -- and this'll mean different things to different people -- you'll start to run into the walls that Apple puts up. It's a very one-sided "my way or the highway" dynamic. It's easier to work around on their laptops, but impossible (or at least unreasonably impractical) on their phones. For context I gave iOS a shake twice, once with the XR and once with the 13 mini.
I've always felt that iOS is the platform you go with for:
- unparalleled high-quality integration with the Apple ecosystem
- a very strongly (and unavoidably) opinionated experience (where the opinions are usually more-or-less correct)