Display back-in-stock widgets for certain products.

Go to edit back in stock config. Scroll to bottom of Settings tab and look for Tags Filtering.

You can use tags to filter products eligible for back-in-stock widgets display.

From Settings > Filtering, specify tags to whitelist or blacklist. 

• If tags whitelist is used, back-in-stock widgets will only be shown if any of product tags matches specified tags.
• If tags blacklist is used, back-in-stock widgets will not be shown if any of product tags matches specified tags.