How confident can we be about what other potential universes might be like with different fundamental constants? Maybe if we pick one constant and vary it sligh

How confident can we be about what other potential universes might be like with different fundamental constants? Maybe if we pick one constant and vary it slightly, we can reason that there would be less carbon, but how do we know that some other combination of parameters wouldn’t create some other phenomenon, unknown in our universe, that could act as the substrate of life? Especially considering we may not know what all the parameters are.