I wonder if carbonated cold brew is a thing in Japan and/or Asia. 25+ years ago I did product testing for a canned coffee beverage. I remember there were many different samples. They were blind, but it was obvious that they varied in levels of sweetness and carbonation. I believe there were also various flavor formulations and I suspected there were multiple levels of caffeine. My vague recollection is that the testing was done in advance of a product release in Japan. At the time, the notion of drinking cold coffee, let alone carbonated coffee, typically seemed very bizarre to those who were sampling it here in the US.