The Google fields can be updated with Stock Sync by using the metafields.


Google Fields
Metafield namespace and key
Metafield Owner
Google Product Category
mm-google-shopping.google_product_category
Variant
Gender
mm-google-shopping.gender
Variant
Brand
mm-google-shopping.brand
Variant
MPN
mm-google-shopping.mpn
Variant
Size
mm-google-shopping.size
Variant
Color
mm-google-shopping.color
Variant
Custom Product
mm-google-shopping.custom_product
Variant
Product Type
mm-google-shopping.product_type
Variant
GTIN
mm-google-shopping.gtin
Variant
Shipping Weight
mm-google-shopping.shipping_weight
Variant


For example:

To know more about metafield click here.