WooCommerce Product Addons Code https://wpsites.net/free-tutorials/product-addons-by-percentage-for-woocommerce/

product-addons.php

add_action( 'woocommerce_before_add_to_cart_button', 'custom_product_addons', 10 );
function custom_product_addons() {
    global $product;
    $product_price = $product->get_price(); // Base price of the product.
    ?>
    <div id="product-warranty-addons">
        <p>Select Additional Warranty:</p>
        <button type="button" class="warranty-addon" data-addon="15" data-price="<?php echo esc_attr( $product_price ); ?>">
            Additional 4-Month Warranty (+15%)
        </button>
        <button type="button" class="warranty-addon" data-addon="30" data-price="<?php echo esc_attr( $product_price ); ?>">
            Additional 8-Month Warranty (+30%)
        </button>
    </div>
    <input type="hidden" id="addon_price_value" name="addon_price_value" value="0">
    <?php
}

add_action( 'wp_footer', 'custom_product_addons_script' );
function custom_product_addons_script() {
    if ( is_product() ) { ?>
        <script type="text/javascript">
            jQuery(document).ready(function($) {
                $('.warranty-addon').on('click', function() {
                    var addonPercentage = $(this).data('addon');
                    var basePrice = parseFloat($(this).data('price'));
                    var addonPrice = (addonPercentage / 100) * basePrice;
                    var totalPrice = basePrice + addonPrice;

                    // Update price display on the product page
                    $('.woocommerce-Price-amount').text('€' + totalPrice.toFixed(2));

                    // Set hidden input value for addon price
                    $('#addon_price_value').val(addonPrice.toFixed(2));
                });
            });
        </script>
    <?php }
}

add_filter( 'woocommerce_add_cart_item_data', 'custom_add_cart_item_data', 10, 2 );
function custom_add_cart_item_data( $cart_item_data, $product_id ) {
    if( isset( $_POST['addon_price_value'] ) ) {
        $cart_item_data['addon_price'] = sanitize_text_field( $_POST['addon_price_value'] );
        $cart_item_data['unique_key'] = md5( microtime().rand() ); // To avoid merging of items
    }
    return $cart_item_data;
}

add_action( 'woocommerce_before_calculate_totals', 'custom_addon_price_to_cart' );
function custom_addon_price_to_cart( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) ) {
        return;
    }

    // Adjust the product price
    foreach ( $cart->get_cart() as $cart_item ) {
        if( isset( $cart_item['addon_price'] ) ) {
            $cart_item['data']->set_price( $cart_item['data']->get_price() + $cart_item['addon_price'] );
        }
    }
}