The one that comes to mind is the Dragonriders of Pern, by Anne McCaffrey. Its been almost 3 decades since I've read them so I'm more than a little foggy on the details, but I clearly remember the story spans several millennia. The series starts out as a science fiction story about colonists landing on a new planet, then facing some global catastrophe which causes the fledgling civilization to slowly regress into a medieval setting.
Well, not really. That's true if you read them in chronological order, but in publication order, the series begins with the original colonists' descendants who've forgotten their origins, giving it very much a fantasy flavor (which is why the books are generally filed as fantasy even though they're actually science fiction). The initial trilogy involves their rediscovery of the origins and true nature of their civilization. Then there's a sidebar trilogy running parallel to the first (with its first two parts coming out between books 2 and 3 of the main trilogy). These were followed by a pair of novels that jumped back 1000 years earlier to depict events that were legendary in the time of the original two trilogies, but still 1500 years after colonization. It was only then that we got the story about the initial colonization of Pern, as the ninth installment in the series. Then there's a tenth book that overlaps and parallels the events of the original two trilogies (McCaffrey loved writing overlapping books), and then the eleventh book finally moves forward from where the original trilogy ended. And the series has continued to jump around in time quite a bit since then.
As for actual magic/fantasy series that move forward into the Space Age, I've always wanted to see something like that myself, but I can't think of any examples. The closest thing I can think of is the animated
Avatar franchise.
Avatar: The Last Airbender was set in a fantasy world paralleling the mid-19th century on Earth, with some parts of the world in a steampunk industrial era while most of the rest was more traditional, and
The Legend of Korra, set 70 years later, parallels the 1920s on Earth, with more modern technology, airplanes, cars, radio, and motion pictures, and an increasingly globalized society.
Korra also did a flashback episode set at the start of the Avatar cycle 15,000 years before and showing what the ancient version of their world was like.
