Heinlein is always great. Check out B. V. Larson's Swarm and Undying Mercenaries series, Dennis E. Taylor Bobiverse series, and Craig Alanson's Expeditionary Force. Also what I mentioned to OP, what I'm doing my annual re-listen of https://www.goodreads.com/series/51166-troy-rising They're not Heinlein by any means but they're fairly good hard science fiction. The audiobook versions all have fantastic narrators too if one has a commute.
Also recommended in this reply