String theory like most of theoretical physics is just made up. Today our knowledge of atomic physics and the cosmos is no more improved little since 1945. There’s a lot of theories, but ultimately they just add up to different kinds of particles interacting in non-verifiable ways. If you look at the actual advancements it’s pretty laughable we’re sitting here saying “Hey look this theoretical thing called a black hole, that easily could just be some type of unknown radio telescope interference? It maybe might exist for a different reason than we thought!” Your layman’s understanding that a black hole is some kinda big suck-y thing in space is actually better then engineering an elaborate and probably incorrect theory.