The basic variant determines the product variant, which can be found in the shop, designer and is to be displayed as the first variant in other places.
You can define the basic variant in the shop administration under the following point: "Catalog -> products -> [your product] -> edit -> variants -> [your variant] -> edit"
Here the item "Set as base variant" and save the variant. Now the desired variant is displayed in the shop overview. Variant is displayed.
In order to publish an article, the basic variant must also be published. be.
More information about this topic: Publishing