Board Thread:Support Requests - Getting Technical/@comment-4286974-20190717100533/@comment-9605025-20190717205546

TL;DR: A pop-up would probably require JS, not CSS. At that point, you could redirect users Discussions. However, since topic and tag selection is done only after the user has provided a title and text, I highly doubt there is a way to pre-fill those fields. The lack of documentation could be for several reasons. However, I believe the most likely one is that there are no customization options for Discussions; it is take it or leave it.

Part of switching from a text-focused encyclopedic format to a social-media-like discussion format is simplifying the user experience and making things easier for new users/admins. As in a lot of cases, this often means removing a lot of user control as it is the only way to ensure a uniform experience across all wikis. The cost of a nice sleek interface and functionality is that wikis will have less and less control over layout and styling.

Given this, I would not be surprised if the lack of documentation is intentional. I doubt there are many, if any, ways to interact with Discussions other than the primary interface. Even if there is, it would probably not be the focus of current development as most people would probably not use it and Discussions is still changing.

You could use custom JS to redirect users from Forum to Discussions; but I doubt you will be able to pre-fill any fields. As soon as you leave "/wiki", custom JS/CSS no longer applies. As such, redirecting the user is the limit of what your JS would be able to do. True, if Discussions provides query parameters for pre-filling fields, then your JS could include those in the redirect URL. However, given that the topics and tags are chosen after the user provides a title and main text, I doubt such parameters are available.