'If a culture with electricity meets a culture with broadswords, the culture with broadswords is a dead culture'. 
If the difference is technological, it seems very unrealistic that societes with a medieval level of technology or less could exist for more than a few years near a society with modern-day levels of technology without being altered. It works if you want to tell the story of a first contact between two different realities, and its consequences. (an example: "The word for world is forest" by Le Guin).
If you go with magic, then you have more choices but you can end with a world very far from your cyberpunk idea.
Maybe a solution could be to make magic or the supernatural dangerous for technology, so that the advanced society would insulate itself from the 'fantasy' surroundings (the fantasy world could even be a sort of 'sealed evil' on a great scale).
Another way is a post-apocalyptic world with a large 'barbarian' landscape and isolated communities which retained an advanced technology. (an example: the film "Zardoz").
I think that the main difficulty is that the two streams (cyberpunk and fantasy) are not only different technologically and socially, but they appeal to very different atmosphere, themes, characters, reasons of conflicts... The only examples I can think of are about different realities clashing against each other, while you seem to look for a unified word and this is way harder. The best advice I can give is to think which atmosphere you want to create, and then to take only those elements which serve your atmosphere, without being chained to a specific setting. For example, if you are looking for a largely inexplored world of adventure just outside your dystopian technological society, then you don't necessarily need a medieval fantasy setting; space opera can serve you just as well.
Lost in Space
Maybe if this cyberpunk dystopia were so completely isolated that nobody else was even aware of its existence, it might work, but you then have to solve the problem of where it gets its resources. You can't just have cities; someone has to grow the food and mine the metals and whatnot.
I can imagine some sort of After the End scenario wherein society is blasted back to the Bronze Age in a catastrophic event, but an enclave of technology survives in an underground city and gradually devolves as it gives up on the outside world. There's a parallel here to the plot of Fallout 4, except that in that game the Institute is more utopian, with technology way more advanced than anyone else, a sterile white aesthetic, and a ruthless vision for the outside world. And the survivors still have plenty of technology.
Of course, the sticking point with an After the End scenario is that no imaginable disaster could wipe out even the memory of a high tech society in less than a few centuries, never mind all the evidence, without being a biosphere-destruction level event.
If you go the other route and insert your dsytopia into an actual historical Medieval society, then suspension of disbelief goes out the window. How did it get there? How did nobody notice? How was there no clash of cultures and technologies?
Edited by Fighteer on Apr 18th 2019 at 4:32:39 AM
"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
Okay so I'm going to stop saying technology to mean things that work based on scientific principles, because otherwise it gets confusing. A major part of my setting is that the technology only works with the permission of the government, and the government knows if someone possesses tech they shouldn't have (it's part of the dystopian theme). So if I go with magic as the source of their technology instead of natural processes, how would I describe in a believable way? What does a magical computer or magical internet look like?
The same as computers and the internet, I suppose. It doesn’t matter to the user whether a car has an internal combustion engine or a magitek clockwork engine under the hood, it’s the same difference either way.
Of course, for stylistic purposes you can add any flair you want.
They should have sent a poet.
One thing that I might add is that the form and function of things may depend on how they developed, and their underlying principles. For example, if the magical internet is based on magic that involves music, you might find that the first communications are audio, rather than text. If the magical computers are powered by enslaved Fair Folk, perhaps there's an undercurrent of rebellious messages going through all the data-traffic. If written words have magical power, perhaps magical computers are operated by hand-writing, and the keyboard never develop. And so on.
My Games & Writing
"Any sufficiently advanced technology is indistinguishable from magic"- to people who do not understand the underlying scientific principles that allow the technology to work. I think what you need is a society that has access to certain specific examples of very advanced technology that they themselves have no idea how they work (I mean they cant manufacture it or reverse engineer the principles involved to modify other technologies, not that they dont know which buttons to push). Imagine a dark ages kingdom that somehow uncovered a modern era weapons cache- they would very quickly figure out how to load and fire the weapons, but might never figure out what smokeless powder is, let alone metal alloys. To them, it's all "ancient magic." So give them the specific technologies that your story requires, and also the technological handicaps that will preserve the setting you want to use, and justify it by explaining that this technology came from someone else, and the knowledge that made it possible was not recovered.
I've been kicking around the idea of a dystopian society that is similar to the modern day, but the society is in a fantasy setting where other nations and peoples are at an Iron Age/Medieval level of technology. I think at its foundation I want to imagine what cyberpunk would look like if it was in a pre-modern fantasy setting. The dystopia has mass media, an Internet analogue that permeates a vast part of society, and advanced cities and infrastructure, but I'm having trouble deciding whether they owe this advancement to technological or magical processes.
If the latter, I think the likely form that it would take is like the Rings of Power from LOTR. People in the society wear and use items that allow instant communication, telekinesis, and a deep level of interaction with the surrounding urban environment.
If I try to just make it technological, my concern is the fact that this is a powerful nation with a wide influence that has existed for at least a whole century. Is it still realistic that other nations won't have adopted the advanced technology? If they use advanced IT and have a complex urban infrastructure, what level of military technology would they have developed as a consequence of the presence of electricity, film and TV, radio waves, transistors, the Internet, etc. (I don't want them wiping the floor with every other nation they encounter)?
Please provide links to any previous threads or topics that you think might be useful to me, and please give any suggestions.