I have tried creating a menu item that points to the actual “forum” itself, but it returns with “page not found”
What is the title/slug of your main forum page. This main forum page should be created via Pages > Add New. At the very least, if you forgot to add the forums index or other available bbPress shortcodes to the main forum page before publishing that page, you’d only get a page with Page title and not a 404 error.
Set up bbPress forums with BuddyPress installs https://codex.buddypress.org/user/setting-up-a-new-installation/installing-group-and-sitewide-forums/
