Easy if you know where to look. If you end up in the wrong sub menu you might simply search the web for instructions.
Apple provides web pages where they explain how to use the iphone. There is a section called "mail" under "apps" that shows up in the search results. It really wants me to read the help in dutch, the "apps > mail" section has 14 pages that don't talk about changing the default app, in stead they explain how to use the various features of their own mail app (that is also configured by default)
I don't get why the help pages need a different menu structure.
One has to go to "personalize your iphone" which has 18 pages, changing default apps is towards the end.
Searching the Dutch help website for "mail" I get only 3 unhelpful search results. If i change it to US English it immediately redirects to Dutch again. lol?
Using the "English" for Latin America and the Caribbean works. There I get 5 pages worth of results. Changing the default app is on page 3.
Not impossible but it is not a simple prompt on launch of the app "Banana mail is not currently your default email client. Do you want to set Banana mail as your default app for sending email?"
I'm quite dense of course, if they are going to be like that I will NEVER create an email client for this platform.
The web and their TOS is full of good reasons to never create an app for iphone.
In a laps of sanity I created a pwa one time. I've explained to exactly one user how to add the option to add a web app to the home screen to the menu so that they can add a web app to the home screen. It was a really hard sell and it took a long time.
I of course had to laugh at myself for acting against my better judgement.
Imagine someone made a web app email client and tried to compete with the build in client. Then in the middle of the struggle apple jokes about discontinuing PWA.
Seems a pretty level playing field?
Actually, at the very top of the home page of the settings app is a search bar. If you type in anything reasonable (default, email, mail) then one of the first 2-3 results will be “default apps” or “default email”.
This is what happens when you install Gmail, for example. You're both under and over-thinking this.