Estaba intentando eliminar python3 presionando el comando sudo apt-get remove python3y ahora todo el sistema está roto. Probé varias soluciones encontradas en Internet, como reinstalar ubuntu-descktop.
sudo apt install --reinstall ubuntu-desktop
el resultado:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
ubuntu-desktop : Depends: gdm3 but it is not going to be installed
Depends: gnome-control-center but it is not going to be installed
Depends: gnome-shell but it is not going to be installed
Depends: gnome-shell-extension-appindicator but it is not going to be installed
Depends: gnome-shell-extension-desktop-icons but it is not going to be installed
Depends: gnome-shell-extension-ubuntu-dock but it is not going to be installed
Depends: ubuntu-desktop-minimal but it is not going to be installed
Depends: ubuntu-session but it is not going to be installed
Depends: yelp but it is not going to be installed
Recommends: gnome-getting-started-docs but it is not going to be installed
Recommends: ibus
Recommends: ibus-table but it is not going to be installed
Recommends: plymouth-theme-spinner but it is not going to be installed
Recommends: ubuntu-docs but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
También intenté reinstalar las dependencias manualmente pero no funcionó.