Kbin needs to be aware of the community first, so my first link didn't work properly because of that. After interacting with the community once the [!community@example.com](/c/community@example.com)
format works just fine. :)
I subscribed from Kbin.social now, so future posts should be visible from there. :)
You should just need to write
[!harrypotter@literature.cafe](/c/harrypotter@literature.cafe)
in the comment box, and the link is generated automatically. Should work in both Lemmy and kbin at least, not sure about mbin but would make sense that it works there as well. :)