Hello there. I'll leave it to others to add suggestions but just a little comment on (quote)
- The explanation how to delete an assignment from https://moodle.org/mod/forum/discuss.php?d=83537 does not work and is heavily outdated but is still part of moodle.org nav tree (Right hand side of page).
I looked to see what you meant by part of moodle.org nav tree (Right hand side of page) Are you seeing the link to that old forum post which is shown in the Navigation block when you happen to be looking at that particular forum/? It's not seen at any other time and the only way to get rid of it permanently would be to delete the thread altogether, but then we'd have to delete all outdated threads in that case.