You can always try out the demo first. It is indeed for smarter people than me :-)

Does the game have a sandbox mode or randomized missions?

I don't recall if there is a particular sandbox mode, however the main missions seem to be the main thing that isn't randomized. Those main missions require certain stuff to be built, as do various other side missions. The main difference between a main mission and a side mission is that the main missions result in story blurbs while the side missions give you resources. The side missions are randomized and make up most of what you do.

I gave the demo a shot yesterday evening but I wasn't really in the mood and did not play far. However, up to that point I don't really see the point of the circuit board layout and it's not really complicated at all. I felt more like an additional chore which did not give me anything in return or allowed me to do additional stuff. I see a potential that additional modules might make it more interesting but as far as I played yesterday, that was just not the case.

I was looking for something to scratch that Factorio itch but from what I have seen so far, that's just not there. I'll try to reserve some time to move further in the demo but if there is more the tutorial should really start introducing that sooner and/or motivate the abstract view better.

Ta to those who replied to me.