limits-comment-length.php

<?php
function my_give_limit_comment_length() { ?>

    <script>
		let comments = document.querySelectorAll('textarea#give-comment');
		comments.forEach(comment => comment.setAttribute('maxlength', 255));
    </script>

<?php }

add_action( 'give_donation_form_after_submit', 'my_give_limit_comment_length' );