Vitamin D is produced during exposure to UV light, any UV light. Sunlight is great for it.
You don’t need to take supplementation for it, you need to make sure that you go out regularly. Even bedridden patients are encouraged to go out for a while every day solely for this purpose. The only real way these days for the vast majority of us to get Vitamin D deficiency is by sitting indoors all day. Spend time outside, it’s free.
The people who have trouble getting vitamin D are people with dark skin, muslim women, shut ins and people in some latitudes where the sun doesn’t rise for months. Even then the problem is solved by spending more time in the sun, stopping the practice of burkha. The few people who need supplementation are people who have issues with this.
Vitamin D is found mainly in animal sources such as fish liver and meat and egg yolk. Some mushrooms contain it but not in the quantities needed.
Just remember, even supplement companies are out for your coin.