P: Ability to assign a second monitor with more than 3 monitors

Finally! Thank you for listening after all these years.

Choose monitor for secondary window

With this release, there is an option to select a monitor for the secondary display when multiple monitors are available. To choose a monitor for the secondary window, do the following:

1. In Lightroom Classic, choose Lightroom Classic > Preferences (macOS) or Edit > Preferences (Windows).
2. Select the Display tab and choose a monitor for the secondary window.

i have 4 screens.  I am a pro photog and I need the real estate when I do post.   I have the very same issue and it's a valid concern for people who use multiple screens. 

interesting discussion here. I find it fascinating that the issue with multiple monitors for lightroom was identified many years ago - because lightroom has two main windows, really, the catalog window and a preview window, it seems mind boggling that Adobe doesn't seem to take the issue seriously. As a photographer you want to be able to use the best display for preview when selecting, and for developing etc when working on a photo. So it must be possible to easily change the monitor each window displays in, why is that still not possible. Simple configuration, or, better, a swap feature on a function key would do it.

My case is that I cannot select which monitor is designated as 2nd monitor. I use 3 monitors. Only 2 monitors are calibrated. I have LR on one monitor and PS on 2nd calibrated monitor. I need to be able to choose which monitor LR uses as 2nd mon. And make 2nd monitor choice skicky please.

When being both a videographer and photographer I am using a 3 display setup on my computer. Windows 10 always assigns the best monitor to be #1, the second best as #2 and the simplest monitor as #3. This is logical since the best monitor with 10 bit display requires highest focus and computer power. 

This also makes sense when running Premiere Pro and After Effects.

When running LIghtroom on the same computer setup, I always want to the second full screen display function in LIghtroom to show up on my best 10 bit display since I am there looking at the details of the photograph in the largest possible format. Lightroom however, always assigns the second display to a monitor with monitor number larger than the main window. Therefore it is only possible to have a second display full screen to show up on monitor #2or3. This means that it will never be on the 10 bit display. 
If floating the 2nd display window it can be dragged to display #1, but when shortly selecting another application for e.g. writing notes, the second display jumps back to the default higher monitor number.

therefore, in order to use LIghtroom in combination with other adobe products on a 3 monitor display, one would like to have a function to select which monitor the second display will show up on. 

I am using Windows 10 with three monitors.
[ 3 ]  [ 1 ]  [ 2 ]
monitor 3 is 1280x1024 (small and not wanted for lightroom) monitor 1 and 2 are both 1080p (big and good)
.
Lightroom forces my secondary monitor to be full screen on the small monitor for reasons unknown. A little googling brought me to this slough of despair thread. Seriously? The devs can't wrangle this?
Is it the case that there is no fix for this common issue affecting so many people?

I forgot to mention that the file extension should be ".ahk" and the first part can be anything you want (i.e. LR_Window.ahk).

And of course it goes without saying, for anyone who didn't read the entire thread, you need to install "AutoHotKey" for this to work.

This is good work. I’m going to try it out.

But, Adobe, notice how users are going to rediculous lengths to just get the windows to arrange correctly on their screens. These customers are worth thousands, maybe tens of thousands of dollars a piece, over the lifetime of our accounts. We shouldn’t have to be programmers to solve this problem.

Hi Ronan,  did you get this working for you?  

Here's a copy of my script, and the only line I needed to modify was the "WinMove" coordinates.   You will need to place this in a text file (use Notepad).

#NoEnv  ; Recommended for performance and compatibility with future AutoHotkey releases.
; #Warn  ; Enable warnings to assist with detecting common errors.
SendMode Input  ; Recommended for new scripts due to its superior speed and reliability.
SetWorkingDir %A_ScriptDir%  ; Ensures a consistent starting directory.

; puth this file somewhere and create a shortuct in C:\Users\<User>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\
; so it starts with Windows
#singleinstance 
#NoTrayIcon
#NoEnv

SendMode Input
SetWorkingDir %A_ScriptDir%  ; Ensures a consistent starting directory.

Loop {
SetTitleMatchMode, 3
WinWait, Lightroom - Secondary Display
;WinRestore
WinMove, 3800, 100 ; adjust this coordinates to suit the screen you want the preview to be
WinMaximize
WinWaitClose
}

As commented at the top, you need to place this script in your startup directory so that it executes when your boot up your computer.   I hope this helps you and others.  

Bruce