Nutrition science is anything but conclusive, however there is some preliminary research indicating seed oils may not be healthy and contribute to obesity. Why are condiments like ranch and mayonnaise unhealthy? Because they're almost entirely seed oils.

There is oat milk without any added oils, including Oatly, but you have to specifically look for that version, they're not always easy to find. And it will taste thinner without any fatty component that cows milk has.