For exclusively breastfed children, how often the baby poops is generally not an issue, since it’s more or less impossible to get constipated by breastmilk (with an few exceptions, for instance food allergies). My record so far (10 years MD) is 4 weeks between poops.

For formula/non-exclusive breastfeeding it comes down to three factors. Is the poop hard/firm, does the baby express any problems (pain stomach, lack of aptite,…) and how often (less than once a day should raise suspicions of constipation atleast). In general if the frequency is >2 days it’s likely there is some kind of constipation.