Url link to feature image in the portfolio [closed]

I think it is possible with custom fields.

Add a custom fields, for example, named link. Put the link into the value field. Then you will be able to access it something like that:

<a href="https://wordpress.stackexchange.com/questions/187970/<?php echo get_post_meta( get_the_ID(),"link', true ); ?>">
    <?php the_post_thumbnail(); ?>
</a>