Enter settings, find the gx corner using the ctrl f, there is a setting that sets it to the sidebar, enable that.

Everyone who still has this issue, I think someone got to it in a previous post, but there are posts after it that still are asking.

Settings: Serach for gx corner. Set it to be in the sidebar.
This removes the gx corner from the tab count, and will let the windows close when you close your tabs, I don't usually have the sidebar enabled, so it works like other browsers for me now.