Maximizing (not fulll screen) safari window in Bug Sur not working (Option Click Plus)
If you hover over green circle while not in full screen you should see following options:

'Zoom' is the option which should deliver result you are calling 'Maximizing the window'. These options are also available under 'Window' on Menu bar (by default keyboard shortcuts are for Tile Left/Right, others must be set).
Shortcut for Full screen is ⌃ + ⌘ + F. Using it while in Full screen reverts window back to initial size before going fullscreen.