This is one of the many plant-based drinks you can make at home.
Soak 150 g of oat flakes in 1.5 liters of filtered water for 24 hours, then blend everything with an immersion blender and, with the help of a food cloth such as etamine, which is used to filter cheeses, separate the liquid part from the oats (which you can then reuse as part of the dough for biscuits, for example). Usually I don't sugar these drinks, so I can use them for both sweet and savory preparations. It lasts in the refrigerator for a couple of days.