You can make essentially any dairy product from breast milk including butter, cheese, Ice-cream, yogurt, etc. there are also several other food products such as breads which can be produced using materials or cultures from the human body.
Many factors can influence milk production levels but an average full production may be around 20-35oz a day total. I won’t explore the reasons why this is not very common beyond to say there are various social/ethical and practical factors that make it so any sort of commercial production especially at scale of such goods is unlikely. At a small scale individual level it is primarily stigma and social factors that make this uncommon- though few households by percent produce their own dairy goods with any sort of milk as a practical matter given the time and details involved compared to the cost of buying such goods ore produced from the milk of livestock, often for far cheaper than can be produced in small batches at home.

So yes, butter can be produced from breast milk but for many various reasons, most people will not ever encounter or consume butter (or other dairy products) made from human breast milk.

Breast milk makes the world turn round.

Thank you <3