The Ubuntu cPanel installer fails to install MySQL on new installations because the gpg-key is never imported. This is due to port 11371 not being open.
Ubuntu cPanel Installer fails to install MySQL because the GPG key cannot be verified. The below will be reported in the cPanel & WHM installation log.
GPG error: http://repo.mysql.com/apt/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8C718D3B5072E1F5
E: The repository 'http://repo.mysql.com/apt/ubuntu focal InRelease' is not signed.
In order for MySQL to be installed as a part of the installation, make sure port 11371 is opened so that the MySQL gpg-key can be imported.