I had a dream once where I somehow was in the far, far future. At first everything seemed like it had regressed or gone back to a more middle ages / middle earth type aesthetic. But then it became obvious that this was intentional - people had rejected a lot of technology and hidden others. So there were many things that did indeed seem like oldschool magic but were actually just powered behind the scenes by some very advanced tech.
This makes for a great writing prompt. In some ways, you're describing the Warhammer 40k universe. The people of that world don't necessarily "reject" technology, but any understanding of it is lost, and things are maintained through ancient relics; the meaning behind which is completely unknown. It's a great fiction premise.
IIRC, One of the alien species in the Stargate series (filling the thematic role of "space elves") appeared primitive because their "technology" was "sufficiently advanced" to the point of being practically magic. I think there were examples in Star Trek as well but I can't remember specifics off the top of my head.
It would be an obvious strategy to hide from the Borg but I don't know whether or not that ever happened. One could imagine a world where complex technology and knowledge was outlawed out of fear of "demons" when their far more advanced ancestors discovered the Borg umpteen thousand years ago and forcibly regressed their society to a more primitive state out of sheer terror, but no one understand the real context behind what's become just a deep cultural fear.
I'm also reminded of the claim by someone in the UFO community - I think it's Robert Bigelow, but it doesn't really matter because it's all bullshit anyway - that UFOS are actually powered by ESP, they aren't even technology in any comprehensible sense, more like technology-shaped talismans that run on the power of space magic and make-believe. It would be hilarious if that were true, and somewhere in the bowels of some ultra top-secret underground base someone is trying to reverse engineer some crashed alien "tech" and being utterly baffled because it literally makes no sense.
