For Construct 3's part, it is very easy, you just export to iOS and you already have an Xcode project, without you even needing to know the technical aspects of what just happened.
The hard part I observe most people get into trouble with is not related to Construct 3, but regarding publishing to iOS.
This is setting up your Xcode project and Apple Developer account. You still need to learn how both of these work and read their documentations.
You also need to be informed about the terms that you've agreed into upon signing up, and follow all the compliances and regulations that are required, otherwise you risk getting banned, not your account but you yourself.
I observe a lot not reading the official Apple documentations, guides and the agreements they have accepted, and get issues down the line.
Hopefully you will research and read the Apple Developer documentation beforehand, so that your publishing will be a smooth process. Please also note that Apple documentations and rules, just like Google's, change often.
Good luck.
Tldr. Construct 3's side is very easy, you just export and you already have an Xcode project. However, most people have troubles with publishing afterwards since all of these processes are of Apple's own documentation and are changing frequently.
Good luck.