Use ‘Gnome Tweaks’ (found in "Software"). Apart from this setting, you can customize lots of the Gnome settings in this app, which is essential to the Gnome DE / Shell IMVHO.
After installing, just go to the "Windows" tab and scroll to the end to find the switch for left/right position of the buttons.
Got answer from https://ubuntuforums.org/showthread.php?t=2348381
Use ‘Gnome Tweaks’ (found in "Software"). Apart from this setting, you can customize lots of the Gnome settings in this app, which is essential to the Gnome DE / Shell IMVHO. After installing, just go to the "Windows" tab and scroll to the end to find the switch for left/right position of the buttons.