I claim zero personal expertise, so will gladly stand corrected by more knowledgeable Manjaroos, but as i recollect, over the years i've read many webpages, posts & opinions on the question of unique /home per distro in a multiboot environment, vs single /home shared across all the distros. I'm sorry but i have an antithetical opinion on this. This diagnosis now interferes with the way that I work, since the option to use the same /home across multiple distros allows me to work relatively uninterrupted when I hit a bug in one environment that isn’t in another. The LibreOffice problem of not showing the Application Menu isn't there, so there must be some deeply-hidden incompatibility on the Thinkpad. Since I have a Asus M5A88-N tower beside my Thinkpad X230T laptop, I've done the most recent updates there. With this workaround, I can at least stay in Manjaro KDE. I had been rebooting into Kubuntu 18.04 for a day. This now gives me an Application Menu in the Titlebar of LibreOffice. I can drag-and-drop the Application Menu into the Titlebar. Selecting on the Buttons pane, the Application Menu isn't in the Titlebar. The Window Decoration options that I've got are for Breeze, Oxygen and Plastrik. I hadn't changed the Widget Style for Breeze. (Under the Manjaro default, was it originally set to Breath?)

The Look and Feel that I have set is Breeze. It's taken me a few steps to figure out how to navigate to the screenshots you've sent. Your suggestion to activate the KDE Application Menu tool is a temporary workaround, so I can at least work with LibreOffice until a longer-term fix resolves. The Global Menu isn't something that I heard of, and I don't think I had set it.

Libreoffice fresh vs still