I noticed that a real dark theme, with a dark color within the window of e.g. the file manager, not only the window title, cannot be installed. I think this has to do with the fact that Lubuntu 20.04 is no longer LXDE, but LXQt.
I tried a workaround by trying to find an .obt editor, but the ones I found on the internet don’t work in LXQt, only in LXDE.
Does anyone know of a working .obt editor, or does anyone know how to implement real dark themes, like the default theme of Ubuntu 20.04, Yaru?