Use a checkbox in checkout page to chose customer send a mail for subscription

functions.php

/**
 * Add WooCommerce Checkbox checkout
 */
function tkd_add_checkout_checkbox() {

    woocommerce_form_field( 'checkout-checkbox', array( // CSS ID
       'type'          => 'checkbox',
       'class'         => array('form-row mycheckbox'), // CSS Class
       'label_class'   => array('woocommerce-form__label woocommerce-form__label-for-checkbox checkbox'),
       'input_class'   => array('woocommerce-form__input woocommerce-form__input-checkbox input-checkbox'),
       'required'      => true, // Mandatory or Optional
       'label'         => 'Ok I agree with <a href="/checkout-checkbox" target="_blank" rel="noopener">Checkout Checkbox Page</a>', // Label and Link
    ));
}

add_action( 'woocommerce_review_order_before_submit', 'tkd_add_checkout_checkbox', 10 );

/**
 * Alert if checkbox not checked
 */
function tkd_add_checkout_checkbox_warning() {
    // its just a check that this function can get the POST value and update in option table.
    if ( (int) isset( $_POST['checkout-checkbox'] ) ) {
        // update_option('CheckoutPage', $_POST);
		$to = 'voboghure.dev@gmail.com';
		$subject = 'Test email from checkout';
		$msg = '';
		foreach($_POST as $key => $value) {
			$msg .= $key . ' : ' . $value . '<br>';
		}
		wp_mail($to, $subject, $msg);
        // We can use wp_mail with POST value for sending mail instead of update_option function
    }

}

add_action( 'woocommerce_checkout_process', 'tkd_add_checkout_checkbox_warning' );