Ubuntu-Mate 20.04 update removes a dialog title bar close button

I updated Ubuntu-Mate 18.04 to 20.04 and all of my LibreOffice dialogs lost their title bar close button. This is a Mate thing. Gnome desktop continues to show the close button. A discussion from several years ago says that some version of Gnome decided to remove this button on dialogs that cannot be resized. Is there a config setting to bring this back? This is similar to but not the same issue as ordinary window title bar min/restore/close buttons.

See this -

which might help solve your problem. Good luck David-McCracken.

Thanks for trying but that refers to a document window rather than a dialog, which is a very different animal even though it too is a window at its core. In that example it appears that the problem was caused by user error. With dialogs, the user isn't even afforded the opportunity to make such an error. Further, the problem that I report does not exist in Ubuntu-Mate 18.04 or in Windows.