Not discouraging further discussion but there are a bunch of questions under our FAQ about the Library of Alexandria so you can maybe check those out and see if anything piques your interest!

The FAQ contains some pretty detailed answers about what lost information might've been in the libary's collection. I'll just note that basic introduction to this topic:

The 'destruction' of the Library of Alexandria has been heavily mythologised into being some kind of seminal event it never was.

It is often portrayed as if the library of Alexandria was the base of an inverted pyramid, without which the whole structure of ancient knowledge came crashing down. The reality, of course, is the opposite, the library was, if you can even speak in such terms, the top of the pyramid encompassing the wide breath of ancient knowledge. The one in Alexandria was just the biggest of plenty of libraries in the ancient world.

Which is why there are several recorded instances of fires in the library, and no real set date as to when it was truly 'destroyed'. The library declined because the socio-cultural foundation it was based on disappeared. The centres of Mediterranean scholarship moving to Rome, Constantinople and eventually Baghdad.

And even if the Library was by some magic preserved from fire. There isn't even much reason to assume any more of its contents would've survived than does today. In the ancient world, 99% knowledge wasn't lost because someone decided it ought to be burned, it was lost because no one decided it ought to be preserved. In a world where everything is written on easily flammable bio-degradable material, it's more a miracle if something did survive than when it didn't. A miracle usually owing either to extreme conditions (see death sea scrolls) or more generally to countless generations taking the effort to continually copy and preserve a work for posterity.