Bring back the custom sidebar width setting [Mac app]

In the Typing Mind Mac app it was possible to adjust the sidebar width via Preferences > Appearance > Sidebar Width for a brief period.

(See "Customize | Fixed Sidebar Widths or Drag to Adjust Custom Width".)

With the release of of the new Sidebar ("Improved Sidebar" on 05.09.2024) this setting disappeared from the Appearance settings.