Could not fetch the package cache information lists - multiple key problems

[xx5yt668b]

===========================
Install Updates Error log
===========================
Install Updates could not fetch the package cache information lists.
Go to https://www.linuxliteos.com/forums/ and paste the log below into a new or existing thread for assistance.

============ Log ===========

Hit:1 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:2 https://brave-browser-apt-release.s3.brave.com stable InRelease
Hit:3 https://packages.microsoft.com/repos/edge stable InRelease
Hit:4 http://repo.linuxliteos.com/linuxlite emerald InRelease
Hit:5 http://archive.canonical.com/ubuntu focal InRelease
Hit:6 https://packages.microsoft.com/repos/ms-teams stable InRelease
Hit:7 https://packages.microsoft.com/repos/code stable InRelease
Err:5 http://archive.canonical.com/ubuntu focal InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
Get:8 http://security.ubuntu.com/ubuntu focal-security InRelease [128 kB]
Ign:9 http://linux.dropbox.com/ubuntu disco InRelease
Hit:10 http://linux.dropbox.com/ubuntu disco Release
Get:11 http://archive.ubuntu.com/ubuntu focal InRelease [265 kB]
Get:13 https://repo.protonvpn.com/debian stable InRelease [2,967 B]
Err:13 https://repo.protonvpn.com/debian stable InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY EDA3E22630349F1C
Err:8 http://security.ubuntu.com/ubuntu focal-security InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
Err:11 http://archive.ubuntu.com/ubuntu focal InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
Get:14 http://archive.ubuntu.com/ubuntu focal-security InRelease [128 kB]
Err:14 http://archive.ubuntu.com/ubuntu focal-security InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
Get:15 http://archive.ubuntu.com/ubuntu focal-updates InRelease [128 kB]
Err:15 http://archive.ubuntu.com/ubuntu focal-updates InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
Reading package lists...
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://archive.canonical.com/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://repo.protonvpn.com/debian stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY EDA3E22630349F1C
W: GPG error: http://security.ubuntu.com/ubuntu focal-security InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
E: The repository 'http://security.ubuntu.com/ubuntu focal-security InRelease' is not signed.
W: GPG error: http://archive.ubuntu.com/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
E: The repository 'http://archive.ubuntu.com/ubuntu focal InRelease' is not signed.
W: GPG error: http://archive.ubuntu.com/ubuntu focal-security InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
E: The repository 'http://archive.ubuntu.com/ubuntu focal-security InRelease' is not signed.
W: GPG error: http://archive.ubuntu.com/ubuntu focal-updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
E: The repository 'http://archive.ubuntu.com/ubuntu focal-updates InRelease' is not signed.

[Valtam]

Menu, Settings, Lite Tweaks, Package System Repair. If that doesn't help, choose a different Mirror for the Ubuntu repositories.

[xx5yt668b]

None of the solutions above helped. Any other way?

[stevef]

Your first post shows the system reporting multiple problems with verifying software.  It is difficult to guess how the system has got into that condition.  To try to work out what is happening, please provide some context about what was happening before the problem started and what exactly changed between the last good update and the first time you encountered a problem ?

Having followed Jerry's suggestion in post 2 please can you rerun the update/upgrade process and post the results back so that we can see what effect (if any) applying the System Repair and then changing repositories has had.

Thank you.