[rickst29]

I am not personally affected, because I only view the TMO forum on a 4K Television "monitor". But this issue occurs in many applications, such as word processors, which often contain right-side "panels" of substantial width. In the case of Word Processors (such as LibreOffice), the contents of these right-side "panels" often provide for additional format controls. But they consume A LOT of horizontal space, and the vertical bar which separates the right panel from the man content is almost universally provided with a tool to show/hide the right panel content.

In TMO forum, the badly designed-panel provides a vertical shrink tool, but the "emptied" panel still wastes the entire panel area with full-width "panel menu bar" with only one menu item on the left, the vertical show/hid control on the right of the menu bar.

ONE 'FIXED' Design (more complex, not recommended):

If the only menu item will always be "Recent Threads", then it's left side label ">>" should be converted into a control. Clicking the control (or swiping it to the right, for the cases of the User viewing and controlling from a touchscreen) WILL shrink the menu bar to be only a small control on the right side, viewed as "<<".

When the right panel's title bar has been shrunk to that small round/square icon, the main "left panel" content width should expand to fill nearly all of the current right panel's width - leaving only a narrow column, containing the control re-enable the "Recent Threads" Panel.

A BETTER "FIXED" UI Design (simple, solves all issues expressed by other persons):

Simply convert the current panel menu's "double-Up" control to be an "X" control, closing the panel and allowing the main content panel to be expanded to the full width of the parent element. (The sidebar would completely vanish.). In order to allow a user to re-enable display of the "Recent Threads" sidebar panel, it can just be added as another menu item within the "Quick Links" menu.

A DIFFERENT AND NEW COMPLAINT:
The fact that the panel contains only 12 thread items, AND is not scrollable, is a separate "problem". The list of Threads should be made scrollable for a much larger number of entries, and it should probably be more tall (maybe 60-80% of the height of the parent element, if fixed... and maybe further enhanced by adding a size control for the panel, in it's bottom right corner.)

These two changes only involved relatively simple HTML/CSS/JS, and I feel that the panel should be enhanced in this way as well.