I've tried enabling/disabling in Behavior "Keep window open when it loses focus" it doesn't do anything. The only way to hide the window is to hit the hotkey (F12 in my case).

Using 3.0.5 under Manjaro.

Using Yakuake 3.0.5 in Kubuntu 18.04 (frameworks 5.47.0, Qt 5.9.5), that feature works fine for me: with the option unchecked then when I open Yakuake with F12 and then move focus to another window then Yakuake hides itself. With the option checked, Yakuake only goes away when i git F12.