@ShionSinX,
in a world where the royalty is the law, if you try to do something like bringing unknown technologies will happen one of two things: you gonna get exploited by whoever manages to get their hands on you (or try to scape from them and live as a criminal, as they are the law) OR you getting your throat slit by those same people. (that is on believable settings, not on shitty ones where the world is pink and everything is fine)
The entirety of western culture revolutionized the world's technology. Again, if what you believe is true about worlds where monarchies are a thing, then why did our current world progress the way that it did? Why didn't people like Aristotle, Divinci, John Dalton, and many many more people who advanced technology and culture in our world do so while also coexisting with monarchies, and yes, sometimes working with them because they were the ones that funded their research sometimes? Why didn't they just get "off'd" if they decided to only work for a university, or for themselves? I know people like to misquote the Galileo situation to attack religion, but Galileo was working for the church who really had no qualms about his research even when they disagreed, the true story is that Galileo mostly got in trouble for mouthing off against the Pope. Had he not done that he would've been fine. Same with Copernicus and his theory, it was actually the scientific community that went against him, not the church (except those scientists that worked for it, yes back in the day scientists worked for the church, but theologically, it wasn't religious people that were against Copernicus or I should say the Heliocentric theory [I'm over simplifying]), not the monarchy, not the kings and queens, etc. Why was it when explorers wanted to explore and they went to people like the Queen or Kings to get funding, they got the money to do so?
I think you're taking a very edgy position on stories like this. I'm going to be transparent. The whole "hide your power thing" isn't my thing either in these stories, especially when these MCs could wave a hand half the time and destroy a whole nation. The whole "hide your power" thing in that situation then becomes kind of stupid (of course, without factoring in several other things like political fallout and if the MC wants to be seen as someone who destroys that easily, etc.) Also, anyone who magically appeared in a Feudalistic Monarchy-like society like this would hopefully have the mental capacity to know they couldn't just be independent. First of all, you have to establish a means of survival unless you're going to just live off the land and then you better hope you're not living off of the King's or Queen's land, or else you're still up crap's creek. The whole be "independent" stuff is a storytelling device and likely wouldn't work in those types of societies for those types of characters. Especially if you take a person from First World culture and dump them in a third-world like society like this. They wouldn't have the first idea how to survive contrary to how stories make it seem, so they'd all likely, yes including you, join up with a monarchy to, at the very least, try to acquire some sort of protective status in on an alien world in a foreign society if they don't have the means for self-preservation, which again, most people that don't fight to survive every day or don't learn that, just don't have those means. Most Isekai MC's are not survivalists nor do they seem to have strong wills or strong ambitions. They are everyday people who authors use to be everymen in the story. They wouldn't survive on their own.
You might say, but they can integrate into that society and still fly under the radar. Okay, the above didn't even get into the fact that most Isekais take place in a European Middle Age setting in which you'd have European looking people and the authors insert a Japanese, Korean, or Chinese Asian looking person into these settings flawlessly and all of the people act like that person doesn't look different than them? Tell me how someone who looks different from everyone flies under the radar from the jump? Not only that, half of the Isekai idiots use their foreign names and don't even think about trying to use a name that fits that society. Again, making themselves alarmingly obviously an outsider. Everyone would immediately know on sight that they don't belong there. So again, this is a storytelling device that too many authors use and too many readers don't think about.
This isn't even getting into stuff like language, everyday practices that would be normal for people of that society, etc. All of which would expose the MC as someone foreign. I respect the stories that deal with this, even if it's marginally as throw-away lines. Even if they give the MC a magic translation device, that doesn't mean everything will translate perfectly. What goes on when MC is moving his/her mouth differently from the words that are coming out of their mouth. You know, like a badly dubbed film. People would notice. There's an abundant amount of things that people would notice to make a MC appear foreign in these worlds, even if they have a European appearance. Things Isekais don't really deal with because then it'd be too nuanced and the authors would have to put some serious thought into worldbuilding, but these are things that would obviously make the Isekai'd person stand out and the whole fly under the radar, hide yourself thing, flies out the window almost immediately when you think about them.
The only way that's going to happen is if the Isekai'd person stays to themselves in the wilderness and hopes they didn't warp into a place that's owned by someone.
Edited to add: In this story's case, MC is not going to fly under the radar selling items from the modern world in a society like this. He is definitely going to catch the eye of some noble, royal, or at the very least, some well-known craftsmen or influential merchant or something. So, again, the whole fly under the radar, hide yourself stuff in this situation doesn't fit.
Its better to live peacefully and do your thing here and there under the radar. Live according to their rules and over time you can expand your horizons w/e way you can with your abilities, but trying to go straight to the top will only get you in bad ways.
Exploring is not trying to go straight to the top and half the time the whole live peacefully thing never works for these MC's because again, no one wants to read about a do-nothing MC. So they almost always end up having some type of adventure or dealing with some type of antagonist, no matter how minor. They almost always end up entangled in some type of politics with the highest person. So again, the whole "stay under the radar" is both unrealistic if this would happen magically to someone unless they're absolutely self-sufficient, which again doesn't necessarily mean they will stay under the radar, and unrealistic for the genre because it never happens.
Thats why on isekais MCs who have the better lives either become normal workers or follow the adventuring road, thats how people on those worlds live normally. The ones that expose their origins and powers quickly become targeted by the bad guys (more often than not, the church and king).
Again, you're basing your argument on current Isekai genre tropes which makes nobility, churches, and royalty bad guys and idiots and overuse the whole MC wants to live in another world peacefully and have a normal life trope. This is a warped view of medieval culture, politics, religious organizations, people, and leadership. That's why it's called a tired, overused trope. In all honesty, if someone appeared in a society like that with power likened to a deity they'd likely be treated like a diety, even by rulers. Even today in our arrogant high-tech society where many believe we've cast off all superstition. Let someone appear with science-defying abilities and they'd likely be treated that way. Sure, scientists would want to study them, sure governments would want to get their hands on them and try to control them. That's natural. But that doesn't mean they can. These things only happen in Isekais because authors make it happen, they write characters that allow these things to happen to them instead of just saying 'no' and dealing with the consequences which may or may not be fighting against that kingdom. Often times in these stories, there are plenty of other kingdoms for the MC to run off to, but they never do because the author forces an attachment to the kingdom they want the MC to be in.
Sorry for making this long, but I've read enough Isekais to know that you have good ones where MCs don't hide their power or don't hide that they're from another world initially or for that long. A good one that comes to mind that I appreciate is Wortenia Senki. MC appeared, beat up those who summoned him, ran away, was chased by the strongest knight in the kingdom that summoned him to be a slave, and escaped to try to find a way back home, but ends up developing his own group that follows him.
Also want to end with my complaint wasn't necessarily about MCs being observant, learning about their world, and trying to avoid joining factions although I made an argument against this. My complaint was about MC's ambition being limited to just wanting to live a normal, slice-of-life type of life, without any ambition to do anything beyond that. Yet, again, the authors never let them do that. Even if they stay on the farm like Isekai Nonbri Nouka, the dude mostly minded his own business but here come dragons, Demon Lords, vampires, Princesses, and Kings bothering him yet he never leaves his territory. Same with Isekai de Tochi o Katte Noujou o Tsukurou, the guy gets tossed to the side, negotiates for land to live "peacefully" and ends up interacting with the Uber Lich, Uber Black Dragon, the Demon King that the Human Kingdom is at war with, the Mermaid Princess whom he marries, and many other things. So his life is not peaceful, nor is it normal, nor is he flying under the radar. Again, never happens. It's just an initial plot device that authors use and then immediately toss away because they know deep down, nobody will read a story about a MC sitting around doing nothing and not interacting with anything.