Spatie\Backup\BackupDestination\BackupDestination::filesystemType PHP Method

    public function filesystemType() : string
    {
        if (is_null($this->disk)) {
            return 'unknown';
        }
        $adapterClass = get_class($this->disk->getDriver()->getAdapter());
        $filesystemType = last(explode('\\', $adapterClass));
        return strtolower($filesystemType);
    }