Thanks! This should work, but I am not sure what address should I use..? Is it "editor.construct.net", project path or what? "editor.construct.net" did not work.
That is what I use and I also use it as an app.
After your post I tested it myself. It seems that this setting has no effect at all.
What I discover is that if you switch to another program with alt-tab it loads in the background sometimes, sometimes not. But what works for me, and this is the reason I thought the setting works, if your program you switch to is in window mode not fullscreen and you can see a little bit of construct in the background it loads the project in the background.
I used to open Thunderbird if I load a project in the background and that is not fullscreen. I have no clue if that works for you but it seems it works for me.