Back in the 90's to 00's a friend had a collection of cd's that he'd written, but he stored them in a big sleeved folder container. The container itself caused them to warp slightly, which made them unusable.
I took a few for testing and managed to unbend them after some time, which turned them back into a working state.
[Note: That's the most apostrophes I've ever used in a sentence, it feels dirty]
https://www.chicagomanualofstyle.org/book/ed18/part2/ch09/ps...
https://www.chicagomanualofstyle.org/qanda/data/faq/topics/P...
If I remember right I just stacked a few starting on the floor with a protective layer in-between so as to not scratch them (a piece of paper is fine). Then add a 5kg or whatever weight on top. After a few days I turned them over and did the same again.
After that most were flat, only one or two needed some more individual time. I imagine that if after that if they're still not flat them maybe heating them slightly in the oven or even just the sun outside might do the trick.
Some kind of 'barcode' encoding, with heavy error correction, would probably be better. I've seen attempts that claim 500kB per side using a largely unmodified QR code system, but I suspect better could be achieved - the method of scanning is probably going to be the bottleneck anyway.
Stone tablets, on the other hand, are rock solid.
(Pun intended)
Unless we could improvise something with old-school dot matrix impact heads to print on clay - I wonder if anyone has tried.