Magento 2 Warning – Count Parameter Must Be Array or Object

It's caused by the fact that your model constructor does not match your original model constructor.

So this is the constructor from Magento\Newsletter\Model\Queue :

public function __construct(
    \Magento\Framework\Model\Context $context,
    \Magento\Framework\Registry $registry,
    \Magento\Newsletter\Model\Template\Filter $templateFilter,
    \Magento\Framework\Stdlib\DateTime\DateTime $date,
    \Magento\Newsletter\Model\TemplateFactory $templateFactory,
    \Magento\Newsletter\Model\ProblemFactory $problemFactory,
    \Magento\Newsletter\Model\ResourceModel\Subscriber\CollectionFactory $subscriberCollectionFactory,
    \Magento\Newsletter\Model\Queue\TransportBuilder $transportBuilder,
    \Magento\Framework\Model\ResourceModel\AbstractResource $resource = null,
    \Magento\Framework\Data\Collection\AbstractDb $resourceCollection = null,
    array $data = []
) {
    parent::__construct(
        $context,
        $registry,
        $resource,
        $resourceCollection,
        $data
    );
    $this->_templateFilter = $templateFilter;
    $this->_date = $date;
    $this->_templateFactory = $templateFactory;
    $this->_problemFactory = $problemFactory;
    $this->_subscribersCollection = $subscriberCollectionFactory->create();
    $this->_transportBuilder = $transportBuilder;
}

To fix your constructor it needs to be:

public function __construct(
    \Magento\Framework\Model\Context $context,
    \Magento\Framework\Registry $registry,
    \Magento\Newsletter\Model\Template\Filter $templateFilter,
    \Magento\Framework\Stdlib\DateTime\DateTime $date,
    \Magento\Newsletter\Model\TemplateFactory $templateFactory,
    \Magento\Newsletter\Model\ProblemFactory $problemFactory,
    \Magento\Newsletter\Model\ResourceModel\Subscriber\CollectionFactory $subscriberCollectionFactory,
    \Magento\Newsletter\Model\Queue\TransportBuilder $transportBuilder,
    \Magento\Framework\Model\ResourceModel\AbstractResource $resource = null,
    \Magento\Framework\Data\Collection\AbstractDb $resourceCollection = null,
    \Vendor\Module\Block\Testing $customergroup,
    \Magento\Customer\Model\ResourceModel\Group\Collection $customergroupdata,
    array $data = []
)
{
    $this->_customergroup = $customergroup;
    $this->_customergroupdata = $customergroupdata;
    parent::__construct(
        $context,
        $registry,
        $templateFilter,
        $date,
        $templateFactory,
        $problemFactory,
        $subscriberCollectionFactory,
        $transportBuilder,
        $resource,
        $resourceCollection,
        $data
    );
}

There is a function available in PHP (>=7.3) which checks if a variable is countable is_countable

Try it like

if (is_countable($bannerGroupData) && count($bannerGroupData) > 0):
    // Your code
endif;

If the function is not available, you can use below

if (($bannerGroupData instanceof Countable) || is_array($bannerGroupData)) && count($bannerGroupData) > 0):
    // Your code
endif;