On orbisius-support-tickets/modules/core/cpt.php file the comment is sanitised as a single-line input with the function sanitize_text_field() which removes the line breaks. For a textarea field WordPress has sanitize_textarea_field();
Ref: https://developer.wordpress.org/reference/functions/sanitize_textarea_field/
On that file, you can find the line
$comment = sanitize_text_field( wp_strip_all_tags( $_POST['comment'] ) );
And replace it with:
$comment = sanitize_textarea_field( wp_strip_all_tags( $_POST['comment'] ) );