Unable to locate ros-melodic on Xubuntu 18.04

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The title speaks for itself, I followed the guide (and the key changing that can be found on different guides online), but I can't install ros melodic due to "Unable to locate package" I'll add all the steps:

luca@luca-lx:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.6 LTS
Release:    18.04
Codename:   bionic
luca@luca-lx:~$ sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'
[sudo] password for luca: 
luca@luca-lx:~$ sudo rm /etc/apt/sources.list.d/ros-melodic.list 
luca@luca-lx:~$ cat /etc/apt/sources.list.d/ros-latest.list 
deb http://packages.ros.org/ros/ubuntu bionic main
luca@luca-lx:~$ clear
luca@luca-lx:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.6 LTS
Release:    18.04
Codename:   bionic
luca@luca-lx:~$ sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'
luca@luca-lx:~$ cat /etc/apt/sources.list.d/ros-latest.list 
deb http://packages.ros.org/ros/ubuntu bionic main
luca@luca-lx:~$ sudo apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
Executing: /tmp/apt-key-gpghome.Yptypss1Bp/gpg.1.sh --keyserver hkp://keyserver.ubuntu.com:80 --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
gpg: key F42ED6FBAB17C654: "Open Robotics <info@osrfoundation.org>" 1 signature cleaned
gpg: Total number processed: 1
gpg:     signatures cleaned: 1
luca@luca-lx:~$ sudo apt update
Get:1 http://security.ubuntu.com/ubuntu bionic-security InRelease [88,7 kB]
Hit:2 http://it.archive.ubuntu.com/ubuntu bionic InRelease
Get:3 http://it.archive.ubuntu.com/ubuntu bionic-updates InRelease [88,7 kB]
Get:4 http://it.archive.ubuntu.com/ubuntu bionic-backports InRelease [83,3 kB]                  
Hit:5 http://packages.ros.org/ros/ubuntu bionic InRelease                                                              
Fetched 261 kB in 3s (83,5 kB/s)                                            
Reading package lists... Done
Building dependency tree       
Reading state information... Done
All packages are up to date.
luca@luca-lx:~$ sudo apt install ros-melodic-desktop-full
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package ros-melodic-desktop-full
luca@luca-lx:~$ apt search ros-melodic
Sorting... Done
Full Text Search... Done
luca@luca-lx:~$

I found that there are some 'ros-desktop' packages, however I can't install them.

I don't know if it's useful:

luca@luca-lx:/etc/apt/sources.list.d$ apt search ros-desktop
Sorting... Done
Full Text Search... Done
ros-desktop/bionic 1.10 all
  Robot OS desktop metapackage

ros-desktop-dev/bionic 1.10 all
  Robot OS desktop development metapackage

ros-desktop-full/bionic 1.10 all
  Robot OS desktop-full metapackage

ros-desktop-full-dev/bionic 1.10 all
  Robot OS desktop-full development metapackage

ros-desktop-full-lisp-dev/bionic 1.10 all
  LISP Robot OS desktop-full development metapackage

ros-desktop-full-python-dev/bionic 1.10 all
  Python Robot OS desktop-full development metapackage

ros-desktop-lisp-dev/bionic 1.10 all
  LISP Robot OS desktop development metapackage

ros-desktop-python-dev/bionic 1.10 all
  Python Robot OS desktop development metapackage

luca@luca-lx:/etc/apt/sources.list.d$ sudo apt install ros-desktop-full
Reading package lists... Done
Building dependency ...