Feynman once had a nice lecture about how the inside of a brick is unobservable. Every time you break open the brick, you see a new surface, not the actual inside. If we have a question about whether the inside actually exists, we can test it in various ways (weighing, grinding it and comparing the volume of the dust to the volume of the brick, x-rays, etc.). If all the tests come out the way you'd expect if bricks have an inside, then you conclude that bricks have insides, even though they are unobservable.
By now, evolution has been tested very, very thoroughly. Pretty much to "inside of a brick exists" levels.
If someone wants to present a theory about evolution not working (or that the inside of a brick not existing), and they want to be taken seriously, they're going to have to also present a test that has a result other than what the current theory (evolution/inside of a brick exists) predicts.