Unfortunately there seems to be a fatal UI bug regarding multiple accounts.
I’ve got several NC accounts activated in Nextcloud app for iOS. But one account has closed. So it was an account for a company during a project.
Now it is impossible to delete this account in the app. Even more after tapping on this account a fullscreen pop-up appears for web login. But with no valid login data it is either impossible to login or to cancel and go back to the app. Even after restarting the app. The only way is to full delete the app and reinstall with all data.
So there must be an option to delete an account without activating it!