The following warning message appears when running apt-key:
apt-key is deprecated. Manage keyring files in trusted.gpg.d instead
The apt-key man page mentions that the "use of apt-key is deprecated,
except for the use of apt-key del in maintainer scripts to remove
existing keys from the main keyring". What's more, "apt-key will last
be available in Debian 11 and Ubuntu 22.04".
Additionally, while the deprecation message says to "manage keyring
files in trusted.gpg.d instead", the Debian wiki states otherwise.
It's recommended to store the keys in /usr/share/keyrings instead,
and then use the 'signed-by' option to reference them.