I would like to second this feature request. iOS client is still not fully integrated with File app in iOS 11/12. Indeed is possible to open files in ownCloud through the File app, but to do so, a pop up windows with ownCloud client is shown INSIDE the File app.
For comparison, DropBox and Google Drive iOS clients are fully integrated with File and could content is shown within File app with the native UI (i.e. without the popup window).
It would very nice to have full integration.
