> Storing books digitally may make them more available in the present, but it will also likely mean that they're be less available at some point in the future. Physical libraries with physical books have proven they can last for centuries, sometimes for millennia.

I don’t k kw about paper books lasting millennia. If you want to preserve books for millennia, you should carve them onto clay tablets and then bake them. The resulting baked clay tablets are pretty durable, even compared to the best paper.