Even easier.

Only buy and eat things with one ingredient.

Vegetables, fruit, meats, beans, rice, etc. you are now eating real food.

That's a simple rule of thumb and matches what I do 95% but there are exceptions like "sugar", "canola oil", "bleached wheat flour" etc.

And there are two-ingredient foods that I do eat, like "peanuts, salt" or "cultured milk, salt, enzymes"