You can get an approximate answer by asking the equivalent question from the point of view of somebody in the year 1900 looking at 2019's technology. Do you have to be beyond smart to be an engineer in 2019?
The answer is no. And there is a very good reason. You may think engineering is about technology and gadgets and doing keen things like building robotic arms for the space shuttle. But those are "extras" so to speak.
The main thing about engineering is managing complexity.
Computer CPUs were mentioned by jedishrfu. When a computer chip gets into the 10's of thousands of transistors on a chip, no single mind is going to be able to comprehend the entire thing all at once. The way that this is managed includes a variety of methods. Some examples are modules, repeating structures, object orientation, and abstraction. You define the component to have an interface. The interface has to satisfy various requirements to fit with the other components. You build the interior of the component, a much smaller and simpler problem, to satisfy the interface, and possibly such things as size and heat load. Then you build the larger system with the standardized components. Even there, you do it hierarchically. The memory is in this zone, the I/O devices over here, the arithmetic unit over there, and so on.
The same kind of things operate in any complicated engineering task. Nobody can hold every detail of the construction of a 100 story building in their head all at once. (Or extremely few people, anyway. Maybe there are a few such people, but I have never met one.) So you get things like a standard floor that gets repeated. And on a standard floor there are standard rooms, hallways, walls, windows, etc. Each of these is divided into components, possibly divided again. Until you get to a simple enough thing that you can hold it all in your mind at once. Then you define how it interacts with other components, and provide methods to test if these interactions are correct.
For example, you build a test wall according to spec. Then you load it up with the weight it should feel in the building and see if it supports it. And you load the connections between the wall and the floor to see if that holds. And so on.
So no, you don't have to be super-duper mutant smart to be an engineer in an advanced tech situation. But the tech has to be designed in specific ways to make it manageable for people who are only a little above average.
