Allow multiple instances (Windows)
On Windows, Ableton Live offers the option Allow Multiple Instances, which you can enable in Live's Preferences tab Display & Input (or Look / Feel in Live 11 and earlier).
This setting allows multiple instances of the Live application to be opened on your computer. It does not enable opening multiple Live Sets simultaneously in a single instance of the application, which isn't possible.
To avoid accidentally opening multiple instances of Live, switch this setting to Off.
Opening multiple instances of the Live application can be used to open multiple Sets simultaneously, for the purpose of cutting and pasting content. However, we don't recommend running multiple Sets at the same time, or actively working in Live with multiple application instances open.
To open a second instance of the Live application in Windows 10, with Live open, double click on the Live application icon. The Live icon in the Taskbar will become "stacked" to show that a second instance is running:
Hovering the cursor over the Live icon in the Task Bar will display thumbnails of open projects: