What is the option for turning off New Window?

[highstream]

Just did a clean install of Win 10 to see if I can overcome crashes that XYplorer and a few other programs have been provoking. After reinstalling XYplorer, I find that it keeps opening multiple windows. What is the option to turn that off? I don't see a New Window entry or similar in Help. Thanks,

[highend]

Configuration | Startup & Exit | Allow multiple instances

[highstream]

Thanks