Ah RIGHT! Yes, to straighten the issue out; The main Library window does remember its size and position, even goes to the correct monitor. I am using Win 10 Pro 64. Here is a screen cap looking remarkably similar to yours. The vertical bar should stay where we put it. It isn't. Grrr. I didn't see anything in that XML file about the Library panel. And from what you said, that doesn't cover the vertical bar. And, that's what the annoyance is. So thanks for straightening me out there. :)

My 66th Birthday PC Build (July 1, 2020) :  named BadMoonRYZEN!, W10Pro x64, Octal Core RYZEN7 X3700 4.05 GHz, 64GB DDR4 RAM, GeForce RTX 3060 - 12GB GDDR6, PP2014, PP 11, P12, PS-CS4 Extended & Vue 2024.

McG.