SkyrimLE:ENBLocal INI Reference/Window
From Step Mods | Change The Game
[WINDOW]
This section is used to enable borderless window with Skyrim. Enabling borderless window can also enable the use of Alt+Tab to run Skyrim in the background.
ForceBorderless
Enables/disables borderless window. This setting forces the game to run in a window rather than as a fullscreen application as it normally would. However, the window will, in fact, be fullscreen and without a border so the appearance of the game, on screen, will not be any different. This enables users to Alt-Tab in and out of the game without issue. Some users have also reported an increase in stability with this mode active.
ForceBorderless=(false, true)
ForceBorderlessFullscreen
This parameter will remove the border lines of the game window when Skyrim is set to Fullscreen Mode. This is best used when down sampling is also used.
ForceBorderlessFullscreen=(false, true)