I'm not really sure what counts as "hard" sci-fi these days, but here's a few of my favorites:

• Fire on the Mountain by Terry Bisson: an alternate history novel where John Brown wins and the South becomes socialist

• The Water Knife by Paolo Bacigalupi: climate change has caused widespread drought and balkanization in the southwestern US, Nevada and Arizona are fighting a cold war over water rights

• Walkaway by Cory Doctorow: fun, optimistic FALGSC story. Radicalized is also good but less hopeful and more violent. Other Doctorow novels are kinda hit-and-miss

• Glasshouse by Charles Stross: a post-singularity mystery set inside a historical re-enactment of a 20th century town. CW: war crimes, body horror, gender dysphoria, and domestic violence. I've enjoyed pretty much everything that Stross writes but Glasshouse is a self-contained story whereas his two major novel series are like 9 books each. Check out The Laundry Files series for Lovecraftian horror mixed with British bureaucracy or The Merchant Princes series for an alternate universe political thriller. Neptune's Brood is also mostly self-contained, features communist robot squids, and was inspired by Debt: The First 5000 Years by David Graeber. Missile Gap is a deeply weird alternate history novella which features Yuri Gagarin piloting a nuclear powered ekranoplan across the flat earth.

• Altered Carbon and its sequels by Richard Morgan: noir detective novels set in a world where human consciousness can be backed up to a computer or put in a new body. Most of the villains are wealthy aristocrats. Too bad the author is a TERF , so steal his books I guess

• Ventus by Karl Schroeder : terraforming robots get out of control and destroy any human technology above a medieval level on a colony world, space cops chase an escaped AI god there and trying to figure out why the robots went rogue. Permanence is another good one about a comet miner who discovers an alien ship and claims it as salvage.