And after eight minutes, the first list is done. And we do, in fact, have the problem with ChatGPT wanting to avoid anything at all NSFW that I thought we might:
* The Heir (Special Edition) – Kayla Eshbaugh
* Of Myths and Portals (Arlan’s Pledge, Book 1) – Jenn Lees
* The Rose Gate: A Retelling of Beauty and the Beast – Hanna Sandvig
* Seeds of Discovery (Dusk Gate Chronicles, Book 1) – Breeana Puttroff
* The Saint’s Magic Power is Omnipotent (Light Novel series) – Yuka Tachibana (translated by Seven Seas)

I haven't read it, but The Saint’s Magic Power is probably closest to what I wanted. All of the books are isekai slow-burn romances, but only two have harems (reverse-harems to get technical). Never-the-less, I'd probably read at least four of these. So kind of a failure at sticking to requirements, but a success at finding stuff I might read? Let's see if I can clarify, and if a nudge will overcome chatgpt's reluctance to engage with certain subject matters.

You said:
Most of these don't have a harem element, or they're reverse-harems.

While we wait for ChatGPT, For comparison, here's a list that Deepseek R1 with Kagi gave me. It didn't ask me for any clarification.
* The Wheel of Time by Robert Jordan: Uh, what? I...sort of...I guess I can see how it got there if I squint. But no!
* The Celestine Chronicles by Cebelius: fits my requirements. I read it, and I strongly disliked it.
* Monster Masseur by Virgil Knightley: I haven't read this one, but Virgil Knightley is an author I've read in the past, and he doesn't fade to black. Ever. At all.
* The Heartstone Saga by Archibald Bradford: never read it, might fit what I asked for.
* Aether’s Revival by Daniel Schinhofen: Yup, right down the line. I've read some of this author's other books, but not this one. Looks like exactly what I wanted, though.

So R1 sticks closer to requirements, accept when it goes wildly wrong. And yet I'd only read two of the books on this list. Is this a case of be careful what you ask for? R1's first try should be a winner, but ChatGPT's books were more of the sort of cozy hole some thing I actually wanted but didn't specify that I wanted that.

And Chat GPT got back to me! It opened with a long AI ramble about how the thing I want doesn't really exist. Incorrect; I've read multiple things that check all these boxes.

Then it gave me:
* Delvers LLC (Series) by Blaise Corvin: Yup. Fits.
* The Good Guys (Series) by Eric Ugland: Eh, I'll give it this one.
* Emerilia (Series) by Michael Chatfield: reading one Chatfield book was enough. Never again. Instead of giving me a book poorly translated from Japanese or Korean, it gave me a book written by an author who writes in English natively, and yet manages to be worse than any translator. Score?
* He Who Fights With Monsters (Series) by Shirtaloon: Yeah, I guess. I read the first few and it never clicked with me, though.

Now over the coming days, I'll read the books I haven't read yet and am interested in, and update the thread. Am I correct that ChatGPT's recommendations are better, but R1's are closer to what I asked for? Stay tuned! Or don't! Or wish this nonsense wasn't appearing in your feed at all! That last is probably most likely.

@alexhall I think He Who Fights with Monsters does get into multiple love interests later in the series? I didn't stick with it long enough to find out. Yeah, Chatfield is the ten realms guy.

Dungeon Crawler Carl...those are the books about Princess Donut and her ever growing harem, right? I think I read those once. LOL

I don't know about love interests in HWFWM. I paused around book 5 and plan to do a re-read in a few years once most or all are out.

I'm re-reading DCC now that book 7 is out. I'm on book 5. Doughnut doesn't have a harem, but Mongo is sure looking to start one. Good timing.