Shrinkflation is largely a myth. Items do not shrink relative to inflation, in fact the majority of claimed products are larger now than they were 50 years ago.
People often cite certain chocolate bar sizes with comparing the size today to that from the 90s. It’s not a fair comparison and not an example of shrinkflation. Mars bars have dropped 20% in size since the 90s but still are 4% larger today then when they originally came out.
Neither are small boxes of cereal. When I worked at Wal-Mart 9 years ago those same thin boxes gave me grief when putting them out on the shelves.