Re: [4.4.2]Error on automated backup, core\task\course_backup_task,array_key_exists(): Argument #2 ($array) must be of type array, null given

This is a current bug we discovered, fix already proposed: https://tracker.moodle.org/browse/MDL-82959

As workaround you can add

$CFG->forced_plugin_settings['backup'] = [];
$CFG->forced_plugin_settings['restore'] = [];

to your config.php