Oat Milk Yogurt- Is Agar mandatory?

Hi,

Trying to make my own Vegan Yogurt/Curd with Oat Milk.

Most recipes call for simmering the milk and adding Agar Agar. Then adding the starter once it becomes luke warm.

My question is,

Is AGAR AGAR mandatory? Will it be too runny if we don’t add it?