Messages d'erreurs en cause (pour faciliter la recherche shaarli) :
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D0184671DE665020
W: GPG error: http://download.opensuse.org/repositories/home:/garloff:/storage/Raspbian_10 ./ InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D0184671DE665020
E: The repository 'http://download.opensuse.org/repositories/home:/garloff:/storage/Raspbian_10 ./ 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

Magique :

apt-key fingerprint D0184671DE665020