May you try to modify line 213 in “/var/www/vhosts/…/httpdocs/wp-content/plugins/qnap-nas-backup/lib/controller/class-qnap-main-controller.php”
from
WP_CLI::add_command( ‘qnap’, ‘QNAP_WP_CLI_Command’, array( ‘shortdesc’ => __( ‘QNAP WP Migration Command’, QNAP_PLUGIN_NAME ) ) );
to
WP_CLI::add_command( ‘qnap’, ‘qnap\QNAP_WP_CLI_Command’, array( ‘shortdesc’ => __( ‘QNAP WP Migration Command’, QNAP_PLUGIN_NAME ) ) );
I guess it’s a namespace problem.