On other computers, I'm using Plasma Desktop where it is quite easy to have a keyboard shortcut that maximizes windows. But I could find a way to do so on Zorin (I have how to enable double click for this but it's much less handy than shortcuts).
Go to settings > keyboard > shortcuts >windows > maximize windows
and set a shortcut you like by pressing the keys.
You can also doubleclick on the titlebar of a window to maximize it (that is the default setting in Zorin Appearance > windows > titlebars, you can also use middle-click or right-click on the titlebar for maximizing the window).