Moving mixer window to my 2nd monitor

Hi, good people,

I have the main Project window on my primary monitor. I want to move the Mixer window outside the Project boundary, and put it on my secondary monitor. But when I try to move the Mixer window, it’s constrained to the borders of the main Project window. How can I “release” it from this constraint, and move it to the second monitor?

If I open effect/synth plug-ins, I can easily move those to the second monitor, no problem, but not the Mixer window. I managed to achieve what I want in some other projects last year, but I’ve forgotten how I did it, and haven’t found a reference in the manual so far.