This code snippet describes how we can Add Featured Image to any Post by custom code,
Just call function add_Featured_Image() with Image URL, and post ID.
This will update featured image to post.
You can add this code to your custom plugin file
or just add in functions.php located in wp-content/themes/your-theme.
Example
add_Featured_Image('https://www.gstatic.com/webp/gallery3/1.sm.png', '1');
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