Magento 2 – Configurable Products Not Showing Shipment Method in Checkout

You should specify Weight in Current Variations grid to make product Simple. If leave this field empty product become virtual

For configurable child product visibility should be 'Catalog, Search'. So when you browse child product you need some custom code. So create a plugin for Magento\Catalog\Controller\Product\View::execute Following way:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Catalog\Controller\Product\View">
        <plugin name="vendor_configurable_product_controller_view" type="VendorName\ModuleName\Plugin\Catalog\Controller\Product\View" sortOrder="1"/>
    </type>
</config>

VendorName/ModuleName/Plugin/Catalog/Controller/Product/View.php

namespace VendorName\ModuleName\Plugin\Catalog\Controller\Product;


class View
{
    /**
     * @var \Magento\Framework\ObjectManagerInterface
     */
    protected $objectManager;

    /**
     * @param \Magento\Framework\ObjectManagerInterface $objectManager
     */
    public function __construct(
        \Magento\Framework\ObjectManagerInterface $objectManager
    ) {
        $this->objectManager = $objectManager;
    }

    /**
     * Product view action
     *
     * @return \Magento\Framework\Controller\Result\Forward|\Magento\Framework\Controller\Result\Redirect
     */
    public function aroundExecute(
        \Magento\Catalog\Controller\Product\View $subject,
        \Closure $proceed
    )
    {
        $productId = (int) $subject->getRequest()->getParam('id');
        $parentIds = $this->objectManager->get('Magento\ConfigurableProduct\Model\Product\Type\Configurable')
            ->getParentIdsByChild($productId);

        $parentId = array_shift($parentIds);

        if($parentId) {
            $subject->getRequest()->setParam('id', $parentId);
        }

        return $proceed();
    }
}

Now you need to select/pre-select JS code. In that case, If you work with magento default 'select' option code then you need to overwrite 'Magento_ConfigurableProduct/js/configurable.js'. Or your case you need to overwrite 'Magento_Swatches/js/SwatchRenderer.js' _OnClick method and add your logic here.