How to add a tab to shop pages?
UPDATE: install Commerce Multistore module and have store/ID/edit, store/ID/products, user/ID/stores views tabs created by default for you

UPDATE: Add store/ID/edit, store/ID/products, user/ID/stores views tabs 

Tabs can be automatically created for you by Views.

WDTutorials video: Tabs With Views in Drupal 8

You have to create a views' page having /some-path  which lists some entities (nodes, fields or products as in your question). Then you need to make it a Default menu tab (parent menu tab). So, if no any child tabs are present then the content for this tab will be displayed. It might be seen a bit confusing but you should choose Already exists option while creating this (newly created) menu tab. After that just create as many duplications of this page as you need and choose for each duplication a Menu tab option (child menu tab). Again, you might be confused which menu or menu entry to choose for children menu tabs. Actually, it does not matter a lot. For your view you may choose Products entry though &lt;Main navigation&gt; menu might be also a good choice. Do not ignore weight option assigning a proper value for each child tab. It helps to place tabs in the exact order you want. Leave 0 weight for the parent tab increasing it by 1 for each next tab.    

Then, edit the path so it looks like /some-path/child-1 and add a filter criteria for a child tab (page). In the video the filter criteria is a node's published/unpublished status and in your case it should be a store ID. The ID of a particular store might be found on the /admin/commerce/stores by hovering over a store's Edit tab.

See more on the relative drupal.org issue:
https://www.drupal.org/node/2880510#comment-12185171