Some good sci-fi that is not (or used to not be) that well known is:

- Children of Time. Really interesting concept that pays off huge.
- Ancillary Justice (and the two other books in the series). Really interesting worldbuilding. Best series since Dune in making human society in the far feature feel strange but yet familiar.
- Murderbot Diaries. Well known now when it has its own Apple show.
- We are legion, we are Bob (Bobiverse books). The first ones are really funny, I haven't read the new ones since I felt they started going into kind of a rut.

Kind of a mashup between sci-fi and fantasy is Dungeon Crawler Carl. It's not exactly unknown considering how much they have blown up. It's a LitRPG, a genre that generally produces utter shit. This series is actually amazing. It's exactly the kind of crude, action based drivel I hate. But I love it. In fact I love it so much I've read the 7 books that are out twice and are now listening to the audiobooks.
By the way, I fucking hate audiobooks. But the guy reading these is some kind of genius and they are genuinely better in this format.
I would describe them as the best kind of junk comfort food. Like if you love hamburgers this is not the fancy burger you get at a decent restaurant. And it's certainly not a shitty burger from McDonalds. No, this is is the greasy burger meal from the mom and pop hamburger joint you grew up with.