Yeah when you start to look into this it's a bit scary. Best bet is something like the M-DISC. But the price per TB is much higher compared to ~15€/TB for HDD it's more like 100€/TB. Plus you need some jukebox like disc switcher.

If there was a collapse of our global industrial society e.g. by disruption of trade and and high tech manufacturing we'll relatively quickly loose much of the accumulated knowledge of humanity. Copyright stuff adds to that. That's why projects like anna's-archive are a moral imperative.

The best would probably be something like a custom microfilm that lasts forever and you can view / play and copy with a primitive projector and chemistry.