I am quite new to Linux desktop and I've encountered some problems with repositories. Whenever I try to update I get a bunch of errors related to public keys in repositories. I've seen there are similar questions related to this, but none of them quite fixes my problem. `
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://ppa.launchpadcontent.net/papirus/papirus/ubuntu lunar InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY E58A9D36647CAE7F
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://ppa.launchpadcontent.net/kubuntu-ppa/backports/ubuntu lunar InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 2836CB0A8AC93F7A
E: The repository 'https://ppa.launchpadcontent.net/webupd8team/y-ppa-manager/ubuntu lunar Release' does not have a Release file.
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.
The way I managed this is by following the "the quick way" on this site https://www.omgubuntu.co.uk/2022/06/fix-apt-key-deprecation-error-on-ubuntu