I still don't know to unfollow a thread where you previously posted, to be more precise how to make that the respective topic won't be listed anymore under "Show new replies to your posts" (in case other users wrote inside those topics).
There's a workaround but it ignores topics by their respective boards:
- Go to Profile > Ignore Boards Preferences [under Modify Profile] > Tick the appropriate board/s > Click Change profile button > You no longer see threads that you've posted in from those boards on "Show new replies to your posts.".
Take note of the following:Be advised that by ignoring a board it will be completely inaccessible to you