Isn't a F11 supported as a shortcut in most of applications to switch to full-screen mode? I remember it was supported over vast majority GUI applications I used, when I was complaining on small screen, but now personally, I don't understand why somebody would need it make windows be maximized-to-workspace as in macOS. There isn't such huge dock, and application menus were redesigned to be in-app-hamburger-menus and finally displays manufactures now provide monitors with higher resolution than few years ago. If you really notice lack of focus / working space, you shouldn't look for typical GNOME/KDE DEs but for a WM (windows managers) like Sway/i3 or AwesomeWM, which helped me to be more productive, when I dab in multiple applications at once.