Why does multi window not work whit my game

[De gekkoboy]

My multi window does not work on games. and if i start a game it says lock recents key enabled. and if i try i see a circle whit a white lock inside.
Ps this is on samsung J5 2017

 

[B. Diddy]

Welcome to Android Central! Does your phone come with a Game Launcher or Game Tools app? If so, open that and see if there's an option to turn that on or off.