Checkout restrict specific products and countries

// Block Checkout
add_action( 'woocommerce_store_api_checkout_update_order_meta', function( $order ) {

	// Settings
	$product_title = 'Product Title Here - Variation Name';
	$pass_countries = [ 'US', 'CA' ];
	$error_message = '
		Sorry, %s can only be purchased from a USA and Canada billing address.
	';

	// Skip Specified Countries
	if( in_array( $order->get_billing_country(), $pass_countries ) ) {
		return;
	}

	// Match Product Title To Cart Items
	foreach( $order->get_items() as $item ) {

		$product = isset( $item['variation_id'] )
			? wc_get_product( $item['variation_id'] )
			: wc_get_product( $item['product_id'] );

		if( ! $product || ! method_exists( $product, 'get_name' ) ) {
			continue;
		}

		// Matched Cart Show Error
		if( $product->get_name() == $product_title ) {
			throw new Exception(
				sprintf( $error_message, $product->get_title() )
			);
			return;
		}

	}

} );

// Classic Checkout
add_action( 'woocommerce_after_checkout_validation', function( $fields, $errors ) {

	// Settings
	$product_title = 'Product Title Here - Variation Name';
	$skip_countries = [ 'US', 'CA' ];
	$error_message = '
		Sorry, %s can only be purchased from a USA or Canada billing address.
	';

	// Skip Specified Countries
	if( in_array( $fields['billing_country'], $skip_countries ) ) {
		return;
	}

	// Match Product Title To Cart Items
	$matched = false;
	foreach( WC()->cart->get_cart() as $item ) {
		$product = isset( $item['variation_id'] )
			? wc_get_product( $item['variation_id'] )
			: wc_get_product( $item['product_id'] );
		if( $product && method_exists( $product, 'get_name' ) ) {
			if( $product->get_name() == $product_title ) {
				$matched = true;
			}
		}
	}

	// Matched Cart Show Error
	if( $matched ) {
		$errors->add(
			'validation',
			sprintf( $error_message, $product_title )
		);
	}

}, 10, 2 );