Use an app full screen
Many apps in macOS, such as Mail, let you expand the window to fill the screen.
Note: VO represents the VoiceOver modifier.
To enter full screen in an app that supports it, press Control-Command-F. You can also navigate to the green full-screen button in the top-left corner of the app window, then press Command-Space bar.
The full-screen button can also expand (or maximize) the window. To do so, navigate to the button, press VO-Command-Space bar to open the Actions menu, then choose “zoom the window.” To return the window to its previous size, navigate to the full-screen button, press VO-Command-Space bar to open the Actions menu, then choose “zoom the window.”
When you work full screen, the menu bar is displayed only when the pointer moves there. To navigate to the menu bar to display it, press VO-M.
To exit full screen, press VO-F2-F2 to display the Window Chooser, press the Down Arrow or Up Arrow key until you hear “Exit full screen,” then press the Space bar. Or press Control-Command-F.