Hi there,
missing fields of aggregate rating
This error is because customers have not rated the product, nor have they left any reviews. If the product has at least one rating, this warning message would go away, and you won’t see the following message.
brand
By default, WooCommerce does not offer brands fields to be associated with individual products. If you want to define brands per product, you would need to install and set up the WooCommerce Brands extension. You can read more on this here: https://docs.woocommerce.com/document/wc-brands/
global identifier
In order to add these values to your WooCommerce products, you would need to install and set up an extension like the Google Product Feed extension. You can read more about this here:
https://woocommerce.com/products/google-product-feed/?aff=10486&cid=1131038
https://docs.woocommerce.com/document/google-product-feed
Mike Jolley, the lead developer of WooCommerce, has tried to summarize these points in GitHub over here: https://github.com/woocommerce/woocommerce/issues/22896#issuecomment-477074896
