Database
db={"EN":[{"_id":"1414","ICECAT-interface":{"Product":{"@Prod_id":"C6614NE"}}}],"csv_import":[{"_id":"ObjectId(\"6348339cc6e5c8ce0b7da5a4\")","index":23679,"product_id":4019734,"part_no":"C6614NE","vendor_standard":"Check Point"}]}
Query
db.EN.aggregate([{$lookup:{from:"csv_import",let:{pn:"$ICECAT-interface.Product.@Prod_id"},pipeline:[{$match:{$expr:{$eq:["$$pn","$part_no"]}}}],as:"part_number_info"}}])