Here is the filter that we added to customize the button attribute.
$cart_btn_attr = array(
'href' => esc_url( $product->add_to_cart_url() ),
'title' => esc_attr( WC_MMQ::getOption( WC_MMQ_PREFIX . 'min_qty_msg_in_loop' ) . " " .$args['quantity'] ),
'quantity' => esc_attr( isset( $args['quantity'] ) ? $args['quantity'] : 1 ),
'class' => esc_attr( isset( $args['class'] ) ? $args['class'] : $class ),
'product_id' => $product_id,
'rel' => 'nofollow',
'attributes' => isset( $args['attributes'] ) ? wc_implode_html_attributes( $args['attributes'] ) : '',
'text' => esc_html( $product->add_to_cart_text() ),
);
$cart_btn_attr = apply_filters( 'wcmmq_cart_button_attr_in_loop', $cart_btn_attr );
Thanks