Continuing the discussion from ISO: Note-taking App that can form a Quick Access Knowledge Base:
When you’d like to make a related post, but don’t want to derail the thread, you can click/tap the time of a post. This opens a little window where you can click/tap
+ New Topic and start a new discussion related to the old one. Like this one
As a bonus, there are links added from old to new, and from new to old.