Sorry for re-sending this, but my Gitlab Kwin fork was outdated and my other MR got blocked because of that. I'm using the Web IDE and there wasn't an easy way to rebase on master. I had to delete the old Kwin repo and create another, and when I did that, the old version of this MR got closed. Sorry for the mess.
As discussed in bug 450270, the option "Include "Show Desktop” Icon" should be enabled by default.
I'm not a dev but Nate said that should be the right value to change. I hope this works.