I really enjoyed the novel Children of Time by Adrian Tchaikovsky. As someone who also thoroughly enjoyed the Expanse this definitely gave me some similar vibes even though the stories aren't similar at all.

Iain M Banks's Culture novels. User name is relevant.

The Hyperion saga is very enjoyable. If you didn't read them already The Martian and Project Hail Mary by andy Weir are outstanding.

Asimov is really good. If you are hesitate you can read I, Robot. Which is a collection of short stories to give you an idea of his writing style.

His books are pretty quick reads and high quality.

I read Solaris recently and was genuinely blown away. Anything from Ursala le Guin is also an excellent choice although I would suggest "the Dispossessed".

If you haven't read the Bobiverse series yet, you're in for a treat. The first book is called We are Legion (We are Bob). The books are easy to read, and somewhat light-hearted, while tackling serious philosophical questions. The first 3 books are right at the top of my all-time favorite sci-fi.

Infinity Gate by M. R. Carey while definitely not his best work (see The Book of Koli trilogy which is outstanding but more dystopian), is a fun multiversal sci-fi romp.