Hi Bar Owner , you can add custom content into the side column by entering it into the Side Column Message box. See this article. You can add quite a lot of content there including images and links, as you are not limited to the initial size of the Message box. The editor also allows you to add custom HTML by clicking the HTML code icon on the left of the editor toolbar.
You may have seen more extensive customization done on other Forumbee client communities. With an Enterprise plan subscription, professional services are available for an additional fee.