As some others have said there is no vegan formula in the uk, it either cows milk or non cows milk with animal ingredients (vitamin D is generally animal derived).
So if you want to raise baby vegan you have to breast fed.
My DS is vegan (6.5 month old), I’m aiming to do extended breast feeding as my breast milk is made for him where cows milk isn’t.
It’s really easy, babies don’t need any milk except breast milk till after 1yr of age and if you need milk to cook with you can use breast milk, oat milk, nut milk or coconut milk. All are fortified with B12.
If you breast fed you need to supplement vit D no matter what your diet is and iron stores deplete at 6 months, again vegan or not. You don’t need meat for iron, lentils, green veg, coconut milk ect are all great sources of iron.
Ethically it’s better to raise vegan until child is old enough to decide when faced with the facts. You can’t undo feeding them dead animals, it’s morally wrong to force a human to consume flesh without their consent.
I don’t know anyone who is vegan that would consider feeding their child animal products unless they had too (ie couldn’t breast fed then totally do what you gotta do).