Can we use one product for multiple display nodes in Commerce D8?
Drupal 8 Commerce does not need product display nodes anymore. When we create a product, we get a page automatically for this product.

But if you need, like me, to keep a "node environment"  on your website then you will have to create as much products as nodes and link them through an entity reference field (Type : Reference > Other...)

To create products, variations and links between nodes and products, I use Feeds, Commerce Feeds and Feeds Tamper. In my case, each feed type is based on upload file technique with CSV file created from Excel.

First, you build a Variations Feed type to create product variations with simple data (sku (unique), price, your_attribute). In my case, customer type was the attribute.

Second, you build a Products Feed type to create products using variations imported before (title (unique), variations (skus), store (required, ID=1 if you have only one). Here goes Feeds Tamper with List explode to get multiple variations for one product.

Third, you build a Nodes feed type to link nodes and products with two data (node title (unique), product title (in entity reference field)).

Finally, you get display nodes with specific products and variations and when you add to cart, products are well separated.

Hope this helps.