Jerud Yes - I use this all the time on Windows. (Though not across multiple virtual desktops… just across multiple monitors…)
Jay implemented support for multiple instances of Legend open at the same time awhile back, but I kept forgetting how to activate it. (I finally put a sticky note on my monitor base!!)
On Mac, the command is: shift+CMD+N
Windows is similar… but I forget the specifics.. and my monitor sticky note is on my work PC. 😛.
Regardless the “New Window” command can be clicked from the File Menu in Legend.