Windows on Parallels 10 with 2 out of 3 monitors only

Using UltraMon seems to work fine for me, I've found it in a post on the Parallels Forum:

I will start the VM with 3 screens, then I use a 3rd party software (UltraMon) and disable the one display so that my VM uses two screens running Windows 7 and my MacOS uses the one.

The best solution is referenced here.

My setup is as follows:

1. Parallels Desktop v15.1.5
2. MacOS Catalina v10.15.7
3. Windows VM running in full screen mode
4. MacBookPro 15" 2018
5. 3 external monitors + the 1 MacBookPro laptop screen
6. One of my external monitors "owns" the menu bar within System Preferences > Displays (this seems to make the MBP screen always appear as monitor #2 in Windows).

Steps:

1. Download (and decompress) the MultiMonitorTool to a folder inside your Windows VM https://www.nirsoft.net/utils/multi_monitor_tool.html. Note the full file path where you save the MultiMonitorTool.exe tool.
2. Open startup folder: Within Windows VM > do Windows Key+R [or Cmd+R] (alternately click start > type "run" > click the run search result)
3. type "shell:startup" in the run textbox > enter (this will open the startup folder)
4. Right click within your startup folder > new > Text Document > rename the document to "TurnOffMonitor.bat"
5. right click TurnOffMonitor.bat > Edit (this will open notepad)
6. paste the following using the path you saved to above (note this disables monitor 2 which is my MBP screen but you may need to adjust this number for your setup):

<path>\MultiMonitorTool.exe /disable 2

7. Save TurnOffMonitor.bat file
8. Start > Power > Reboot your Windows VM
9. upon startup, it should disable whichever monitor is marked as #2

If your unsure what number your monitor is, run the MultiMonitorTool.exe > top pane > look at the "Name" column which has the monitor #.