skygiants

Riddle-Master is post-apocalyptic?

Yes. It's post-apocalyptic fantasy rather than science fiction, which I think camouflages it, but it is explicitly stated that gur jnef bs gur Rnegu-Znfgref zber be yrff erfuncrq gur cynarg: "Gur ernyz nf lbh xabj vg jbhyq abg unir ynfgrq gjb qnlf va gur sbepr bs gubfr onggyrf. Jr enmrq bhe bja pvgvrf. Jr qrfgeblrq bar nabgure. Jr qrfgeblrq bhe puvyqera, qerj gur cbjre rira bhg bs gurz . . . V fjrcg [gur Rnegu-Znfgref] vagb gur frn juvyr gur rnegu fybjyl urnyrq vgfrys." Praghevrf gb zvyyraavn cnffrq orsber uhzna frggyrzrag ortna, va gur ehvaf bs gur Rnegu-Znfgref' pvgvrf, xabjvat fbzr bgure phygher unq pbzr orsber gurz, abg xabjvat jung raqrq vg. Gung xabjyrqtr vf fgvyy pbaprnyrq ng gur fgneg bs gur svefg obbx; vg guerngraf crbcyr'f yvirf. I read these books so young, it took me years to notice the depth of time in them and on some level just how weird they are.

I wonder if a better question might be whether there's fiction like this that isn't post-apocalyptic in some way or another?

It's hard to get the conditions for a total societal reset otherwise.

Though as I have just said that, I think a lot of white people I know right now are waking up to the poisoned lies that have underlain America since it was founded, so perhaps you only need an apocalypse for some part of the population, not the entire culture.