As I've already mentioned in this topic, the name you've mentioned is NOT the username, it is a Member Mention Nicknames.
https://wpforo.com/community/how-to-and-troubleshooting-2/problem-with-answer-button/#post-31999
You can hide the Mention Nickname in Dashboard > Forums > Settings > Features admin page.
I don't want to hide the Nickname, I want to hide the Display Name next to posts. Not the Usename as mentioned before, sorry for that.
So far it's possible to show both I think, the Display Name AND the Nickname next to posts, right?
How can I hide the Display Name?
Thanks and best regards
Christian
Thank you very much it worked! But now there is another problem: when one of the users replied with quoting the original post, (so the other post is at the start of their reply) then there is a line above the text "Posted by: @username" and that's a problem because I want them to see the display name of other users not the username. How can I change it to the display name? Or if I can't do that, how can I block these type of replying?

