Not sure this is the right place to put it, this is not a question but just to share the tip.
There's a bug in gedit that lets the close button hidden when it is set to the left of the title bar and when the left panel is enabled in the same time. It looks like the close button, or the entire title bar, is gone. This is annoying because you have to close gedit using the menu from the right. Not efficient!
And so, a fix for it has been published here: https://github.com/rastersoft/gedit_closebutton
It works perfectly fine.
It took me some time to finally find the solution and I think it deserves to be known or found quicker by anyone having the same problem.
Have a nice day!