Thanks to all the KDE devs for their work.

Something I use a lot on xfce4 is the Alt-F11 shortcut (it toggles) that maximises a window over the bottom bar and removes the title bar.

In this way, with LibreOffice or say Inkscape I get the application menus at the top and the applications controls at the bottom of the screen. No hotspots - nothing pops up.

On Fedora's live KDE iso I can use the window control menu to supress the title bar on a maximised window and I can hide the bottom bar but its a faff requiring multiple steps.