$collection = $this->_productCollectionFactory->create();
$collection->addAttributeToSelect('*');

$categoryData = $this->getRequest()->getParam('whoisitfor');

// Get category selected.
if(isset($categoryData)) {
    $categoryData = $this->expandFormValues($categoryData);
    $categories = [$categoryData];//category ids array
    $collection->addCategoriesFilter(['in' => $categories]);
}

$collection->addAttributeToFilter('user_experience_level', array('eq' => 3003));

$collection = $this->_productCollectionFactory->create();
$collection->addAttributeToSelect('*');

$categoryData = $this->getRequest()->getParam('whoisitfor');

// Get category selected.
if(isset($categoryData)) {
    $categoryData = $this->expandFormValues($categoryData);
    $categories = [$categoryData];//category ids array
    $collection->addCategoriesFilter(['in' => $categories]);
}

$collection->addAttributeToFilter('user_experience_level', array('eq' => 3003));