Logicomix [1]. It's a nice comic book focusing on the formalisation of mathematics, starting at the end of the 19th century. This was a foundational quest to solve paradoxes such as the Russel paradox [2]. This also rised questions such as "can everything be proved"?
A math history book about one specific area of study written more in a popsci style that I liked: one of my favorite authors (David Foster Wallace) wrote "Everything & More: A Compact History of Infinity" which I'd call a 7/10 pop math experience and a 6/10 DFW experience, which is still a pretty good deal.
If you're no Math PhD but you are mathematically inclined (e.g. I studied plenty of math as an undergraduate but left to play the software industry game thereafter) you should have the errata document handy (I'll link the parent page that has other paratext [1]) - the author is a math enthusiast but not a mathematician and gets some of the finer details incorrect.
I also read Fermat's Last Theorem by Simon Singh and recall liking it, but I can't recall if it holds up under either mathematical scrutiny or the scrutiny of a more refined palate.
You might enjoy "Excursions in the History of Mathematics" - Israel Kleiner.
It's sort of inbetween popsci and Graduate Maths, probably undergrad level. Lots of historical "essays" covering Number Theory, Calculus/Analysis, Proofs etc..
Has some interesting history - apparently Newton developed three versions of his calculus: infinitesimals (geometric approach), fluxions (kinematic approach) and 'prime and ultimate ratios' (algebraic). He used a mix of all three to solve some problems. Never read that before!
"Journey through genius" by William Dunham. It's not comprehensive, in the sense that it selectively samples the evolution of math from antiquity to about the 20th century, but it fits the bill of a pop-sci book that also shows the real math (at about a high school level) while covering the history and personalities involved. I've read it several times and really enjoy it.
Edit: I clicked though and I see that (for me) William Dunham is actually the author of the first article in the list.
Many people have been inspired by this book and it is entertaining. But in terms of history it is notoriously inaccurate, and some parts are just made up to make it more exciting.
Something not really for general public, but also not for math PhD.