@ksen
when they talked about the train at a museum, I took this she did have a passing interest in how things work, and if you have even a modicum of interest, you can find blueprints/patent info/even entire shows that go though it step by step.
Now if you bring the concept of magic into this, then you side step the years of trial and error that would come from not knowing exact mechanics and more knowing the ideas.
Now as for modern looking, that's likely all it is, is modern looking. note the expression on anyone's face besides the maid, even the mc seems to have issues with the cars at times, now I have been in some old cars where even going 40 miles an hour was scary and you felt everything, and I have been in fairly high end luxury cars where at some point you realize you were accidently going 80 because you felt nothing at all. my best guess here is that the cars just look modern.
as for why everything is so basic elsewhere. you don't see it to much in modern times, but you need 1 person with a vision and a means to advance things, look at the idea of an assembly line. there are a few basic ideas I had, that are very simple, kind of no shit ideas, but no one has ever made something so when I did I technically became an inventor just because no one ever made the shape I did before. I mean you have easy access to the materials, you have a problem, but no one ever came up with a painless solution till I did. in software you see this more often then mechanical now, something that was very obvious but just wasn't done before for some reason, and it takes either someone with the means to do it, or the backing to have it made. for a free thing, look at hydrus, a personal image repository, some programs tried to do this in the passed, but nearly all failed, and this is the first viable program for it.
but i'm not looking at magic creating different thing, im looking at magic taking the roll of something more difficult. the example here was the combustion engine was to hard to make so they went with a magic alternative. depending on how much space that takes up, you could instead of a mechanical solution for 4wd, you could have a magic one where you have 2-4 engines for the wheels.
as far as I remember, and as far as I have seen in the raws for the manga, nothing is really immersion breaking from an 'I call bullshit on you having this' kind of thing.
Some of this comes from making guitar pickups and also making speakers because it seemed easy and I wanted to try, and it is, its very easy if you know what to do but would have likely been a nightmare to figure out if it never existed before, but the principles behind it are all, at least in my education, 2nd to 3rd grade concepts, granted we never got practical uses out of what we were doing, but the concept we learned then would also extend into wirelessly charging a battery/induction cooking ect.
you have an mc who has seen blueprints, who knew a dead sea was likely a salt source, both of these suggest she had an interest, and you have very early life knowledge that if you have a photographic memory and all the time in the world to thing, you could apply it to recreate things if not had off the concepts to people who can do the trial and error portion themselves.