WordPress is a content management server, and not an app.
You won’t get WordPress itself or some other content management system as an app without running a web server (embedded or otherwise) on an iPhone or Android device, and either porting or migrating to a content management system for that web server or web framework, and that server-oriented usage not a very good fit for mobile devices various reasons.
You can potentially wrap access to a web server into an app, though you’ll want to check with the WordPress folks for suggestions there or for the preferred way to do that. Basically, running an app that’s not much more than a web browser at its core. Apple iTunes does this for some of its operations, as do some other apps.
There are examples of wrapping the Safari browser into an app available in the Apple developer documentation.
https://developer.apple.com/design/human-interface-guidelines/ios/views/web-views/
https://www.spaceotechnologies.com/create-web-browser-wkwebview-ios-tutorial/