Just like gravity, evolution is both a fact and a theory.
Gravity-as-fact: we can observe that things fall down.
Gravity-as-theory explains the mechanism causing them to fall.
Evolution-as-fact: we can observe that evolve.
Evolution-as-theory explains the mechanism causing them to evolve.
That is the way science works. We observe some facts and then develop theories to explain the mechanisms behind those facts.
Every time an insect evolves immunity to an insecticide we can observe evolution-as-fact.
This is only incompatible with some overly literal interpretations of Genesis. As has been pointed out, those interpretations are allowed, but not mandated, by the Catholic Church.