I’m assuming from your tags that you’re using Gnome DTE. Have you installed Gnome Tweaks from Software? If not, I recommend giving that a try. Once installed, open it and search for ‘focus’ or go right to the Window section and set the focus as you’d like.
Before I steer you further from you desired goal, are you using the Gnome DE (Desktop Environment - I apologize for the incorrect abbreviation used previously)? If so, is a graphical (GUI) solution to your question acceptable, or are you set on editing a configuration file either from the command line or a graphical editor? As has been mentioned, more info would be helpful.
Gnome Tweaks is a GUI configuration tool that allows a user to customize the DE easily. You can find out more about it online.