Ошибка при обновлении в терминале

rinka@rinka-pc:~$ sudo apt-get update
[sudo] password for rinka: 
Get:1 https://repo.steampowered.com/steam stable InRelease [2,852 B]
Err:1 https://repo.steampowered.com/steam stable InRelease                     
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F24AEA9FB05498B7
Hit:2 http://archive.canonical.com/ubuntu focal InRelease                      
Get:3 http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu focal InRelease [17.5 kB]
Hit:4 http://security.ubuntu.com/ubuntu focal-security InRelease               
Hit:5 http://ph.archive.ubuntu.com/ubuntu focal InRelease                      
Err:3 http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu focal InRelease     
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 531EE72F4C9D234C
Hit:6 https://repo.protonvpn.com/debian stable InRelease
Hit:7 http://ph.archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:8 http://ph.archive.ubuntu.com/ubuntu focal-backports InRelease
Reading package lists... Done
W: GPG error: https://repo.steampowered.com/steam stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F24AEA9FB05498B7
E: The repository 'https://repo.steampowered.com/steam stable InRelease' is not 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: GPG error: http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 531EE72F4C9D234C
E: The repository 'http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu focal InRelease' is not 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.
rinka@rinka-pc:~$