Add Minimize and Maximize Buttons in GNOME
GNOME Tweaks tool allows you customize various aspects of GNOME. Enabling minimize windows buttons is one of them.
Install GNOME Tweaks tool using your distribution's package manager first.
Run the application and go to the Windows Titlebars from the left sidebar. You'll see the options to add minimize and maximize buttons here, You can choose either or both. If you don't want it anymore, you can disable the buttons the same way in GNOME Tweaks tool.