The missing menu bar on LibreOffice (and Electron apps) has been the source of a headache to me for a few months. I’ve been adding/removing packages and enabling/disabling preferences, but nothing seems to work.
Recently it occurred to me that I could enable Libreoffice’s Notebookbar as a menu bar replacement, which can be enabled from the Tools menu… which is not accessible due to the missing menu bar. Even trying to access Tools by pressing Alt+F12 did nothing.
I then remember that the missing menu bar only occurs on Xfce, not on MATE, which I still have installed as a secondary DE. So I logged in to MATE, opened LibreOffice, turned Notebookbar on, and returned to Xfce.
The Notebookbar still looks a bit off to me, especially when Libreoffice’s not on full screen, but it’s better than nothing.