Can Mutations Ever Be Beneficial?

Darwin's idea was that these variants arise by chance, but if they make the organism better adapted to use a technical term, then they will tend to be more successful. The individuals carrying those organisms will have more offspring. And then the mutation will get more and more common in the population. So mutations can be beneficial. Most of the time, they either don't have any effect or they're bad for us, but sometimes they are beneficial. It sees chance mutations that arise that then increase in frequency because they confer an advantage on the organisms that carry them. There's an incredible amount of genes and incredible data in these tests. How certain can we be if a result comes back that is fact