Depends what you mean by "mass market" - it could mean a whole range of things.
Maybe my tastes are more "obscure" but lately
No Longer Human by Osamu Dazai has gained some notoriety because of Pewdiepie and BookTok. (I liked it before it was popular

). It's one of the best classics ever written.
I guess there's also other books that are widely available like Mary Shelley's
Frankenstein. That's a great novel. That fits your science fiction request. Also basically the entire bibliography of H.G. Wells, J.R.R. Tolkien (don't watch the Amazon Prime show, I don't consider it canon), even to some extent J.K. Rowling's
Harry Potter.
Lemony Snicket's
A Series of Unfortunate Events fits that vibe well, too. Non-propagandist, no pornography, just a fun, long adventure.
I really do not know if you'd consider many of these "mass market" but they are widely available.
If you're looking on the Kindle store - don't, period. Coming from someone who's had relative success on Kindle via my own publishing. 99% of Kindle books are smut and generally poorly-written.