On this article we have a cool functionality on Confluence that is only available on the old editing experience.
This functionality consists into create a link to a page that doesn't exist yet, letting the link text as red and, when clicking over the link, you are redirected to a draft page with the title you set on the undefined link, in order to create the page.
On the new editing experience, this functionality is missing. It would be great to bring this to our product again
As this is not a native feature in the new editor for now, we can keep using our undefined links by opening them on a new tab (right-clicking over the link and selecting this option, or CTRL + Right Click / COMMAND + Right Click).
To insert an undefined link on a page with the new editor, create a link with this address: