What Comcast services do you have? For Peacock, you must have either TV service, or a Flex box (you don't even need to use the Flex box if you don't want to.)
As noted, you must have some form of TV service. On another site, somebody did add in a Flex box, and Peacock was immediately available, even though they don't even have the box yet, and will probably put it in a closet and never use it. From what I read, the Flex box is free.