How to install gui on Lightsail instance running Debian 11 ?

Official Debian guidance on Desktop environments can be found here: https://wiki.debian.org/DesktopEnvironment

The specific Desktop Environment pages each provide guidance on CLI installation of the desktop.

• Gnome: https://wiki.debian.org/Gnome
• Plasma by KDE: https://wiki.debian.org/KDE?action=show&redirect=Plasma
• Xfce: https://wiki.debian.org/Xfce
• LXDE: https://wiki.debian.org/LXDE
• MATE: https://wiki.debian.org/MATE