Microsoft Office applications on Windows behave like Mac OS - if a window does not have input focus, then clicking one of its buttons only focuses the window and you have to click again to activate the button (or other control).
This would be annoying enough if it was consistent with other apps, but it's not even consistent with other Microsoft apps like Explorer.
This post "First mouse click sets focus but is otherwise ignored" describes the problem well but the moderator didn't get it, and it has been ignored.
This one "Windows requires a click to activate a window before a second click will select a button. How can I change this?" was about developing code rather than general user configuration.
One workaround is to enable "Activate a window by hovering over it with the mouse" from the Control Panel, but that is not to everyone's taste and changes the behaviour of the whole desktop rather than just fixing the broken apps.
Is there a way to stop Office apps ignoring click on unfocussed window without changing the behaviour of the whole desktop?