Lubuntu default keyboard shortcuts for always on top, normal, maximize
Lubuntu default shortcuts can be found at
https://help.ubuntu.com/community/Lubuntu/Keyboard#Keyboard_shortcuts
Others must be configured by each individual user.
F11 toggles a so-called full-screen display.
As it leaves tabs & menus on if used on a browser, this is rather a toggle-maximize rather than a toggle-fullscreen.