Tagging Product Variants
Shopify platform supports tagging at product level but not at individual product variant level. Due to this limitation, Auto Tags can't help tag product variants, although you can tag products based on variant level conditions e.g., inventory quantity, SKU, size, colour, etc.
This is very limiting and lot of merchants using Auto Tags app struggle with this limitation by Shopify platform. If Shopify decides to add support for tagging at product variant level, we'll be more than happy to support this functionality in the app.