My father told me he wanted to make USB flash drives of all the scanned and digitized family photos and other assorted letters and mementos. He planned to distribute them to all family members hoping that at least one set would survive. When I explained that they ought to be recipes to new media every N number of years or risk deteriorating or becoming unreadable (like a floppy disk when you have no floppy drive), he was genuinely shocked. He lost interest in the project that he’d thought was so bullet proof.
Archival grade m-discs, apparently. I had the same question. https://www.howtogeek.com/858426/whats-the-best-way-to-store-data-for-decades-or-centuries/
https://www.amazon.com/s?k=archival+mdisk
It’s a shame their capacity lags so far behind current hard drives. And not many drives for these discs are still made, so what are the chances of them becoming unreadable just because no one has equipment to read them?
Cool! I can see how optical media could, in theory, be very long-lasting as long as you don’t use materials that oxidize or otherwise degrade over time.