I’ll throw in my 2 cents. Children of time is a good trilogy, especially if you like biology but the 1st book was the best with each following book being weaker than the last. Definitely worth reading though as it scratches that hard sci-fi itch.

I’d also add the Remembrance of Earth’s Past trilogy to this list, it’s the only series that almost matches The Expanse in terms of pure greatness IMO. I read them a few months ago and I find myself thinking about the concepts and ideas introduced in the trilogy every few days still. Absolutely amazing books that any sci-fi fan should try. I will say that the characters are for the most part, pretty boring and don’t come anywhere near the greatness of The Expanse’s characters. It’s the main complaint I see about those books are the fairly dull characters. The ideas and concepts the trilogy introduces are absolutely fascinating though, even better than anything from The Expanse IMO and it easily makes up for the lackluster characters. It’s also fairly hard sci-fi like The Expanse and relies a fair bit on semi-realistic (for the most part) science like The Expanse does. Beware that these books have a fairly pessimistic view of the universe, but that’s also what helps make the books so good.

I’ve gone back to The Three Body Problem multiple times since my first read just so I can re-read my favorite scenes from the book and those books almost single handedly reignited my love for space. I can’t recommend them enough.