Hello, a bit of an old post, but I am facing the same issue. I am running the function using ‘load_field’ and although the field is set as ‘not required’ and this is reflected on the output html, after submitting the form I can still see an error.
function acf_classified_date_required_change( $field ) {
$field['required'] = false;
return $field;
}
add_filter('acf/load_field/name=classified_date', 'acf_classified_date_required_change');