Either you want to breastfeed or you do not and the question ends there and then.
The baby depends solely on you for food, warmth and connection. It's a biological imperative. You either provide or you don't.
Debating if a fluid your own body produces to fullfil the needs of another life you - hopefully! - willing and actively created is anything but nonsensical.
When I replied your question directly I did it after reading the entire thread and every interaction you already had.
Neither me nor anyone is in a place to tell you what to do or think, so my answer was cut down to tangible facts.
Your child depends on you, solely, for food, warmth and protection. If you do not feel at ease with breast feeding, that is up to you. Why I do not need to know nor anyone else. What you should keep in mind is that your child does not judge you nor it pays any consideration to trivialities like you posed in your question. Your baby trusts you fully and absolutely.
If breast milk is vegan or not, as a question, to my understanding, is an exercise in stupidity.
You, as an individual, a person, a human being, are not stupid.
Personally speaking, breast feeding will always be better than providing synthetic formula. Unless a mother has any impedement to do so, it's the best source of nourishment for a child. Formula is normally produced from cow milk, highly processed, and "fortified" with so much additives it should be considered a chemical product, not food stuff.