Combined Listings is new feature designed for Shopify Plus store owners, enabling you to
Benefits of Combined Listings feature:
You have two ways to use this features:
If you want to use an existing Product Group, go to the ‘Product groups’ tab, click the dropdown beside ‘Edit’, and choose ‘Convert’ to convert that product group to Combined Listings.
If you want to start fresh with a new group, go to the ‘Combined Listings’ tab, click ‘Create Combined Listing’.

Option values: The Swatch Display Style defines how the swatch appears on the storefront
Two colors swatch on the storefront
Click the + icon to add a new product.

NOTES:
When your chosen products are in another group, a small window will pop up like this.
If you click ‘Publish’, the combined listings will be automatically published right after.
Click ‘Save draft’ or 'Save' if you want the combined listings to be hidden on the live store.
👉 How to add the Combined Listings Widget:
* A warning will appear when you create a combined listing : “Add the Combined Listings Widget to this product template.”
First, click on Add Widget.
The widget will be automatically added to the Product information section on the Product page.
You can also add the widget by yourself. Under the Product information section, click on “Add block”, type in “Combined Listings” and add this widget.
The widget will appear on the product page as in the below image.
NOTES: It is required not to delete the theme’s default variant picker, as the Combined Listings Widget works in conjunction with it to display product options correctly. 
Pro tips: Experts suggest that when testing combined listings, you should set the product status to “Unlisted”.
“Unlisted product status hides products from store search and collections, all sales channels, internet searches and Shopify Catalog—while still allowing access via a direct URL. It’s ideal for private sales, warranties, add-ons, or “free gift with purchase” items you don’t want discovered or used outside of their intended purpose.” (Shopify)
A parent product generated by ‘Combined Listings’ should be added details for better Shopify SEO.
To make changes, on the dropdown of your combined listing, click ‘View in Shopify’.
Here, fill in specific information about your parent product: title, description, images, metafields, etc.
Now you know how to create a Combined Listing to enhance your store's display and search power. If you need any support on this, we are here to help.