To redirect Add to Cart on all products to same external link, you can use this code to Website Tools > Code Injection > Footer.
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.1/jquery.min.js"></script>
<script>
$(document).ready(function(){
$('.sqs-add-to-cart-button-wrapper').click(function() {
window.location.href = 'https://www.google.com';
});
});
</script>
Replace Google with your desired url
