Como posso corrigir erros de chaves ausentes?

Como posso corrigir erros de chaves ausentes?

Eu realmente preciso da sua ajuda como um novato em Linux :/

Eu apaguei a pasta trusted.gpg.dlocalizada em /etc/apt/e também apaguei /etc/apt/sources.list.d.

Agora, quando tento atualizar, recebo estes erros:

Err:2 LINKpt.archive.ubuntu.com/ubuntu focal-updates InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY **<My_Key_Missingg1>** NO_PUBKEY  **<My_Key_Missingg2>**
Err:3 LINKpt.archive.ubuntu.com/ubuntu focal-backports InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY **<My_Key_Missingg1>** NO_PUBKEY  **<My_Key_Missingg2>**
Err:4 LINKpt.archive.ubuntu.com/ubuntu focal-security InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY **<My_Key_Missingg1>** NO_PUBKEY  **<My_Key_Missingg2>**
Err:5 LINKppa.launchpad.net/webupd8team/y-ppa-manager/ubuntu focal InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY **<My_Key_Missingg3>**
Get:9 LINKmaven.xwiki.org stable/ Packages [352 kB]
Reading package lists... Done
W: GPG error: LINKpt.archive.ubuntu.com/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY **<My_Key_Missingg1>** NO_PUBKEY  **<My_Key_Missingg2>**
E: The repository 'LINKpt.archive.ubuntu.com/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.
W: GPG error: LINKpt.archive.ubuntu.com/ubuntu focal-updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY **<My_Key_Missingg1>** NO_PUBKEY  **<My_Key_Missingg2>**
E: The repository 'LINKpt.archive.ubuntu.com/ubuntu focal-updates 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: LINKpt.archive.ubuntu.com/ubuntu focal-backports InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY **<My_Key_Missingg1>** NO_PUBKEY  **<My_Key_Missingg2>**
E: The repository 'LINKpt.archive.ubuntu.com/ubuntu focal-backports 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: LINKpt.archive.ubuntu.com/ubuntu focal-security InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY **<My_Key_Missingg1>** NO_PUBKEY  **<My_Key_Missingg2>**
E: The repository 'LINKpt.archive.ubuntu.com/ubuntu focal-security 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: LINKppa.launchpad.net/webupd8team/y-ppa-manager/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY **<My_Key_Missingg3>**
E: The repository 'http://ppa.launchpad.net/webupd8team/y-ppa-manager/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.

OBSERVAÇÃO -Alterei http:// para LINK para poder enviar esta pergunta.

Eu tentei um monte de sugestões como:

1 – apt install extundeletepara recuperar os arquivos. E receba este erro:E: Unable to locate package extundelete

2 - sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com --recv-keys **<MY KEY>**(já tentei com e sem hkp://)

3 - apt-get install ubuntu-keyringe erros semelhantes sobre NO_PUBKEYS

4 - gpg --keyserver pgpkeys.mit.edu --recv-key **<MY KEY>** gpg -a --export **<MY KEY>** | sudo apt-key add. e recebi o erro:gpg: keyserver receive failed: End of file; gpg: WARNING: nothing exported gpg: .: read error: Is a directory gpg: no valid OpenPGP data found.

5- Já usei esse também sem sucesso sudo apt update 2>&1 1>/dev/null | sed -ne 's/.*NO_PUBKEY //p' | while read key; do if ! [[ ${keys[*]} =~ "$key" ]]; then sudo apt-key adv --keyserver hkp://pool.sks-keyservers.net:80 --recv-keys "$key"; keys+=("$key"); fi; done

Alguém pode me ajudar, por favor?

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