Up-vote for the Well World books! I remember them fondly. It’s been 40 years – might be time for a refresher :) Now I see he wrote two more in the series in 1999/2000? I had no idea. Suppose I have no choice now

Those were f*cked up but also great. The reveal in “Well of Souls” was so good.

Fantasy+Sci-fi - Timothy Zahn has a couple (Triplet comes to mind), as does David Brin (The Practice Effect). Also well worth mentioning C.S. Friedman’s “Dark Fire” trilogy.

Magic/science crossovers I can think of offhand…

The Madwand series and the Amber series by Zelazny. Actually Lord of Light may sort of qualify too? He was big on mixing the two. Roadmarks is another one.

There’s also people writing about magicians living amongst us. Stuff like the Unseen University by Naomi Novak. Very much traditional magic but also taking place in the modern world. Same for An Unkindness of Magicians by Kat Howard. Actually one of the very best from this genre is The Magicians by Lev Grossman.

I also love Strata by Terry Pratchett which is a suitably hilarious take on building a flat planet where magic works in a science universe.

And another idea I really enjoy is books that have applied the principals of science to magical systems. Probably my favorite is The Craft Sequence by Max Gladstone. Magic is basically something like a stock market/economic system and you end up with index funds of souls and so forth. Very strange but fascinating to think about. Similarly Foundryside by Robert Jackson Bennett is all about using magic as a system and developing new spells based on known principles of that system. (And using them to steal things.)

We’re not there just yet, but Brandon Sanderson’s Cosmere books will be blending magic and tech as they go on. He keeps promising to deliver FTL travel using the magic systems he’s embedded in his worlds.

Without getting spoilery, the Cosmere is a shared universe for the majority of his book series and novellas. Each series deals with a magic system that was “splintered” in a way from a main source of divine power. While each series or novel is pretty well self contained, they more you read the more you notice overlaps between the series; it’s possible for powerful and talented beings to travel between worlds in the Cosmere without going through space.

Each of his main series has tech developments and time jumps built in where we see tech developing more and more. In one series, he has three or four eras planned, with the first and second eras already published. The first era is your typical dark fantasy setting, and by the time of the second era “magi-tech” (or “fabrial” tech might be a better in universe term) has developed to be about old west levels. The next era is supposed to be at a 1980s tech level, and I think the last era will be future tech.

There have also been indicators that beings that are aware of more than one planet in the Cosmere being concerned about tech level and the rate of technological progress occuring in a given world. There might be a conflict brewing in which a magi-technological arms race matters, so each series is getting a healthy injection of tech development.

All that is to say, don’t pick up a book set in the Cosmere today and expect robots and spaceships. But the current work is all clearly laying the foundations for such. Might take a few more years to really get there, but Brandon is nothing if not a prolific author.

Gideon the Ninth is necromancers in space. It’s written as a scifi, but the necromancy is a hundred percent magic, not science veiled in mysticism.

Also, The Traitor Baru Cormorant is a hard fantasy. Which isn’t what you asked for, but it’s similar in that it blends both genres.

My first exposure to sci-fi + magic were the Shadowrun novels. I enjoyed reading them years ago, but not sure how well they’ve held up.