How are you a Moderator? This is an opera shortcut, it doesnt work on chrome, firefox, or edge. If you even tried to help you would of tried or googled if you even could do it on other browsers, or came across this post (https://forums.opera.com/topic/28906/closing-tab-using-shift-click) from your very own forum. There are other post like that scattered throughout here from the past years, but nobody seems to know a real fix.