I am using MX linux.
Libre office opens under the left hand menu bar more commonly called a panel. I have to grab it and move it to the right to use it. I want it to open to the right of it.
LibreOffice is not doing the windows management - which is done by the operating system’s window / desktop manager. And you did not mention what MX Linux does use (KDE, GNOME, MATE, Xfce, LXDE, Cinnamon, or what else might be out there …). So I’d assume you won’t get a decent answer without that information.
BTW: Just started an MX Linux ISO (Version 19.3 / Xfce desktop) and I can't seem to recognize what you mean - LibreOffice (version 6.1.5 installed by default and probably from a Debian repo) Window perfectly fits into the desktop and does not overlap with other desktop elements. Hence providing a screenshot might be helpful.
MX Linux uses XFCE by default. That is what I am using on this computer. When I open Calc for instance, I only see about half the row number column on the left. The left part of that column is under the panel. I always have to grab the top of Calc and move it to the right to use it.
Opening more windows of Calc usually means more of Calc is under the panel. Often I can’t get to the function I need immediately because it is too far to the left under the panel.
By the way this is using a personal snapshot of MX from another computer to install the O.S. The snapshot originally had the panel at the bottom but after re-installation on this computer I moved it to the left. I also had to reverse the placement of many of the items in the panel because they were at the wrong end of the panel. I wonder if this has something to do with the problem?