When it comes to the milk, the truth is, you don't even have to add it at all. But most people enjoy milk or cream in this dish, so let's talk about substitutes. If you want to add it.
Most dairy-free milk has a specific flavor. So you'll want to consider that when choosing the type of milk you want to use. The "blandest" dairy-free milks are typically unsweetened almond milk or unsweetened oat milk. You can certainly try others, but chances are they will add flavors you don't want. And of the two, I would opt for oat milk for the best flavor. Believe it or not, the way we eat this dish in America isn't necessarily how it's eaten in Italy. There, you can find it made without any milk or cream at all. Just lots of butter and parmesan cheese. So feel free to omit it if needed. Use tofu and blend it smooth with other ingredients in a blender. While I don't personally eat tofu anymore, it's definitely an option for many vegans. Use cashews to make a blended sauce. A high-powered blender is very helpful for this option. Use vegetables to create a substitute cream that is quite delicious and definitely more friendly to the waistline.