The auto-close function was related to the GSX Toolbar icon that opened the Menu, and it was there to save you from many double-clicks (one to close the toolbar icon and another one to re-open it), since in the previous version, the only way to open the Menu was a click on the Toolbar icon.
Now there's an hotkey, you only need to activate the GSX Toolbar icon with a click the first time, than it will stay open until you click it again so, for as long as you need ground services, you can use the Hotkey to open/close the menu as required so, once the Toolbar is Active, GSX will work as it always did in FSX/P3D for the past 10 years.
Maybe you assumed something completely different, like a PINNED menu, but that's not what this update is about. A pinned menu is a completely new feature that will require some major changes to how GSX works, and it has been already confirmed to arrive in a future update:
https://www.fsdreamteam.com/forum/index.php/topic,27778.0.html