I had the same void to fill after finishing The Expanse series a couple years ago. But I was also still on a bit of a sci-fi “high”.
A quick series that I jumped to afterwards was The Bobiverse. It has a more casual writing style, but entertaining in its own way. I especially liked the first couple books. You and I seem to have similar tastes, so you might consider jumping into the first book to see what you think. ( the exception of strong disagreement on HHGTTG 😁, though I can understand your comment on first vs second half)
The Andy Weir books suggested by others are also great reads, but surprisingly, I would recommend them as audiobooks… because they are even better listens if you are into that. I rarely do audiobooks, but The Martian and Project Hail Mary are hands down the best listening experiences I’ve had. Typically audio doesn’t have the same charm as reading, but I have no hesitation suggesting a listen to those two!
The Last Human by Zack Jordan and Recursion by Blake Crouch were a couple nice one-off reads that had some fascinating themes as well. There were things I didn’t love, but still not bad as a transition if you didn’t feel like jumping into a whole new series.
For a recommendation totally out of left field, sounds like you enjoy deeper fictional world building. You would likely enjoy the fantasy book The Name of The Wind by Patrick Rothfuss, but prepare for epic disappointment when you find out the third book of the trilogy isn’t released, and may never be written.
The narrator for Project Hail Mary does a great job, so maybe that will be helpful to get through the opening act. Once the meat of the story picks up, it’s pretty awesome IMO.
I’m in the same boat for Game of Thrones… Everyone says I’ll love it, but I can’t bring myself to dive in knowing it won’t be finished. Honestly, I wouldn’t have read Name of the Wind had I known, but the person who recommended it failed to mention the trilogy wasn’t finished! That being said, it leaves a lot of room for imagination, and really inspires more reading when you get to the end of book 2… with a healthy dose of utter frustration.