While reading the forum, I found that Vendors cannot publish Blogs.
In all six demo pages that we can see on your demo page, Blogs from different Vendors are published. As presented, on these demo pages there are Vendors, Listings with the names of these Vendors and Blogs with these Vendors names. For me, this is a clear demonstration of the functionality you offer with this plugin, where users Vendors publish Listings, Requests, Replays, Offers, and also Blogs. If your plugin does not offer the ability for Vendors to publish News (Blogs, Posts), why did you decide to somehow disguise it in the demo presentation and then later simply write that you do not support it?
Showing the blog page is common for any WordPress theme demo, as this is core WordPress functionality. It’s used to show the posts layout and styles, sorry if vendor names appearing on posts was confusing – we just set different authors for posts, so the demo content looks less generic, and the only users registered on the demo site were vendors.
It’s still possible to allow users or vendors to submit posts to your blog:
If you don’t block access to the WordPress dashboard and you have trusted/verified vendors, you can place a link to the WordPress back-end posts page somewhere – vendors would be able to see only the Posts menu item and submit Posts via the same editor; each post would require admin approval.
Since the blog is a core WordPress functionality, you can use a plugin to add the post submission form to your site, for example, this one User Submitted Posts – Enable Users to Submit Posts from the Front End – WordPress plugin | WordPress.org. This way, you can add a new page (e.g., “Submit an Article”) to allow users/vendors to contribute to the blog on your site. This option is more secure as it doesn’t require unblocking access to the WordPress dashboard.