Desktop Environments (DE), or the Graphical User Interface (GUI) you use with it. Essentially you can choose the graphics set and layout of your computer. The underlying functionality of your computer doesn’t change too much, but how things get displayed does. Ubuntu by default uses GNOME. but you can install Kubuntu instead of or alongside it and use the KDE environment. I used to have both installed and just chose which one I wanted to use at the login screen. Eventually I moved to the i3 environment as well and would switch to that sometimes because it could be fun to play with. If you’re new to this and use Ubuntu I’d just start with that (GNOME) and then you can branch out from there when you feel ready. KDE runs a bit more efficiently but looks a bit simpler, last I used it.

Not averse to the idea, but why so? What’s the advantage?

Yeah outside of Java I’m wondering if I might have to start learning some OpenGL/Vulkan stuff for graphics.