Condless

WooCommerce plugin that sets default attribute for variable products automatically if only 1 option is in-stock.
<a href="https://en.condless.com/default-attributes-for-woocommerce/" rel="nofollow ugc">Documentation</a> | <a href="https://en.condless.com/contact/" rel="nofollow ugc">Contact</a>
Variable product of T-shirt with color attribute (White/Blue/Black) and size attribute (S/M/XL): 
If only Black T-shirts are in-stock: default color (Black), default size (none). 
If only Small T-shirts are in-stock: default color (none), default size (Small). 
If only White and XL T-shirts are in-stock: default color (White), default size (XL).
<h4>How It Works</h4>
<ol>
<li>Before product variations is displayed to the customer, the plugin will check each attribute, and if there is only 1 in-stock option it will be set as the default.</li>
</ol>
<h4>Features</h4>
<ul>
<li>Stock: Set option as default when it’s the only 1 in-stock.</li>
<li>Per Attribute: Set specific option as default in all products with that attribute (from the Edit Attribute screen)</li>
<li>Top: Set as default the first option of each attribute.</li>
<li>Out of stock: Disable out of stock variations.</li>
<li>Add to Cart button: In archive pages display for variable products the attribute name instead of: “Select options”.</li>
<li>Select options: In single product pages remove the select options text if default attribute is set.</li>
</ul>

Default Attributes for WooCommerce

WooCommerce plugin that sets default attribute for variable products automatically if only 1 option is in-stock.

isabel104

This is an extension for WooCommerce that will show your custom product attributes on the single product page above the “Add to cart” button instead of in the “Additional Information” tab. Your product attributes will also be displayed at several other locations, including on order emails. See the full list, below. This plugin does NOT affect nor include attributes which are used for Variations.
Your product attributes will also be displayed at these locations (with option to turn them off):
<ul>
<li>Cart page</li>
<li>View Order page on front end for customers</li>
<li>Emails that goes to the customer, including:
<ul>
<li>Receipt (Order Processing) email that goes to the customer</li>
<li>Order Complete email that goes to the customer</li>
<li>Customer Invoice email</li>
</ul>
</li>
<li>New Order email that goes to the administrator</li>
<li>Admin Order Details page on the back end, under Order Items</li>
<li>Grouped product page</li>
<li>Shop page (including product category and tag archives) (Off by default. You must enable this option on the settings page.)</li>
</ul>
See the <a href="https://isabelcastillo.com/docs/woocommerce-show-attributes" rel="nofollow ugc">full documentation</a>.
Languages
If you want to translate this plugin to your language, you can do so easily <a href="https://translate.wordpress.org/projects/wp-plugins/woocommerce-show-attributes" rel="nofollow ugc">on this page</a>. After you submit a translation, contact me in the support forum to request approval as a Translation Editor.
Disclaimer
I am not affiliated with WooCommerce or Automattic. I provide this plugin as a free service to the WP community because of the many requests that I received for it.

WooCommerce Show Attributes

Show WooCommerce custom product attributes on the Product, Shop, and Cart pages, admin Order Details page and emails.

Default Attributes for WooCommerce vs WooCommerce Show Attributes