Add text below WooCommerce short description if metabox value is true

Following the suggestion by @1inmillion, I put the second filter inside the first IF statement, which works nicely.

This is the combined code:

// 1. Add text below short description
function bja_product_unavailable_text( $content ) {
    $content .= '<div class="bja_product_unavailable">This product is unavailable</div>';
    return $content;
}

// 2. Remove add to cart button if product is set to unavailable and add text below short description
function bja_replace_add_to_cart_button($purchasable, $product) {
    $product_unavailable = get_post_meta($product->get_id(), '_product_unavailable', true);

    if ($product_unavailable === 'on') {
        $purchasable = false;
        add_filter('woocommerce_short_description', 'bja_product_unavailable_text', 10, 2);
    }
    
    return $purchasable;
}
add_filter('woocommerce_is_purchasable', 'bja_replace_add_to_cart_button', 10, 2);