So I’ve got my forum set up, but once I click on a certain topic, the category/blog sidebar is the default and even though I’ve tried to change the sidebar in my page builder, it seems like I can’t get this category/blog sidebar off. If there a way to change the side bar menu that displays when viewing individual topics?
Your theme is probably just displaying topics in the standard single.php template. Assuming you're using a child theme, I suggest duplicating the single.php template and renaming the copy to single-discussion-topics.php. The theme will then use this template to display topics - so you can edit or remove the sidebar.