So, I was doing sudo apt update and it asked me if i wanted to overwrite some mirror-related thingies. Like, it.archive.ubuntu.com was switching from FOCAL to FOCAL BACKPORTS or something like that.
I pressed Y, the default value, and it asked me to re-do sudo apt update.
Here is what apt is saying.
nicolo@nicolo-pc:~$ sudo apt update
Get:1 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Err:1 http://security.ubuntu.com/ubuntu focal-security InRelease
Splitting up /var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_focal-security_InRelease into data and signature failed
Ign:2 http://it.archive.ubuntu.com/ubuntu focal InRelease
Hit:3 http://repository.spotify.com stable InRelease
Err:3 http://repository.spotify.com stable InRelease
Splitting up /var/lib/apt/lists/repository.spotify.com_dists_stable_InRelease into data and signature failed
Hit:4 http://ppa.launchpad.net/zorinos/apps/ubuntu focal InRelease
Hit:5 https://repo.steampowered.com/steam stable InRelease
Get:6 http://it.archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]
Ign:7 http://ppa.launchpad.net/zorinos/drivers/ubuntu focal InRelease
Get:8 https://packages.zorinos.com/stable focal InRelease [9.406 B]
Ign:9 http://ppa.launchpad.net/zorinos/patches/ubuntu focal InRelease
Get:10 https://packages.zorinos.com/patches focal InRelease [15,5 kB]
Ign:11 http://ppa.launchpad.net/zorinos/stable/ubuntu focal InRelease
Hit:12 http://it.archive.ubuntu.com/ubuntu focal-backports InRelease
Err:12 http://it.archive.ubuntu.com/ubuntu focal-backports InRelease
Splitting up /var/lib/apt/lists/it.archive.ubuntu.com_ubuntu_dists_focal-backports_InRelease into data and signature failed
Get:13 https://packages.zorinos.com/apps focal InRelease [9.404 B]
Hit:14 http://it.archive.ubuntu.com/ubuntu focal Release
Hit:15 http://ppa.launchpad.net/zorinos/drivers/ubuntu focal Release
Get:16 https://packages.zorinos.com/drivers focal InRelease [18,2 kB]
Hit:18 http://ppa.launchpad.net/zorinos/patches/ubuntu focal Release
Hit:20 http://ppa.launchpad.net/zorinos/stable/ubuntu focal Release
Reading package lists... Error!
W: GPG error: http://security.ubuntu.com/ubuntu focal-security InRelease: Splitting up /var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_focal-security_InRelease into data and signature failed
E: The repository 'http://security.ubuntu.com/ubuntu focal-security InRelease' is no longer signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://repository.spotify.com stable InRelease: Splitting up /var/lib/apt/lists/repository.spotify.com_dists_stable_InRelease into data and signature failed
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://it.archive.ubuntu.com/ubuntu focal-backports InRelease: Splitting up /var/lib/apt/lists/it.archive.ubuntu.com_ubuntu_dists_focal-backports_InRelease into data and signature failed
E: Clearsigned file '/var/lib/apt/lists/it.archive.ubuntu.com_ubuntu_dists_focal-backports_InRelease' contains unsigned lines.
E: The package lists or status file could not be parsed or opened.