magento2 – Specific attribute for the new product collection of Magento 2

I want to create a new widget for products that will be available soon.

A toggle attribute will be available shortly.
I found sample code online, but none of the answers contain file paths.

How would I create this collection? (ie code correction and especially in which file)

Code that I think will work:

 _productCollectionFactory = $productCollectionFactory;    
    parent::__construct($context, $data);

public function getProductCollection()
    $collection = $this->_productCollectionFactory->create();
     $collection->addAttributeToFilter('coming_soon', array('eq' => 'coming_soon'));

    return $collection;


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