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


Google FieldsMetafield namespace and keyMetafield Owner
Google Product Categorymm-google-shopping.google_product_category
Variant
Gendermm-google-shopping.gender
Variant
Brand
mm-google-shopping.brand
Variant
MPNmm-google-shopping.mpn
Variant
Size
mm-google-shopping.size
Variant
Colormm-google-shopping.color
Variant
Custom Productmm-google-shopping.custom_productVariant
Product Typemm-google-shopping.product_typeVariant
GTINmm-google-shopping.gtin
Variant
Shipping Weightmm-google-shopping.shipping_weightVariant


For example:

To know more about metafield click here.