Hi Sebastian

Yes, there is! - but it's super secret and you mustn't tell anyone about it...

It looks like as of Umbraco V9.5 this PR was accepted into the Core:

https://github.com/umbraco/Umbraco-CMS/pull/12116

This introduces the concept of a 'SendingAllowedChildrenNotification, which is issued whenever somebody goes to create a new node underneath a node...

and this notification contains a list of all the types of things that the current editor is allowed to create... and you can 'check who is logged in' or 'check to see whether a certain node has already been created' and modify the list of things that the editor is allowed to create...

The example in the PR description shows checking for a 'Settings' node and not allowing it to be created if it already exists:

public class TestCode : INotificationHandler<SendingAllowedChildrenNotification>
    {
        public void Handle(SendingAllowedChildrenNotification notification)
        {
            var children = notification.Children.ToArray();
            if (children.All(it => it.Alias != "settings"))
                return;

            var currentSettings = notification.UmbracoContext.Content.GetSingleByXPath("//settings");
            if (currentSettings is null)
                return;

            notification.Children = children.Where(it => it.Alias != "settings");
        }
    }

The old way still works of allowing a Settings node to be created and then you create it yourself, then disallow it from being created again... but this programmatically way would allow infinite possibilities, only allow people to create a certain type of page on a Wednesday for example....

https://docs.umbraco.com/umbraco-cms/reference/notifications/sendingallowedchildrennotifications

regards

Marc