I’ve created several new topics in Plex Media Server > Desktops and Laptops > server-windows in the last 7 days.
When I go to that section of the forum and click on My Posts, sometimes I see all my posts and sometimes I see only older posts (5 days ago). It is not consistent.
If you mean make a new topic you need to enter a category that you think the topic you want to make belongs in. If you want to discuss something about your server then open the server category. If about a player then open the player category. The NEW TOPIC button will be at the top when in a category