Is it true: Library of Alexandria Destruction?

There's no solid evidence for it.

The claim assessed here is that the Library of Alexandria was destroyed in one catastrophic event, whether by Julius Caesar, Bishop Theophilus or the Arab conquerors, or was deliberately wiped out to suppress knowledge. No single destruction has been established, and nothing in the sources supports a suppression plot. The Great Library of Alexandria (Mouseion) was established c. 3rd century BC by Ptolemy I and did suffer real losses: (1) The fire Caesar set to ships in the harbor in 48 BC spread ashore, and several ancient writers report losses but disagree on what burned. Caesar's own account mentions only ships and the docks, Seneca reports forty thousand books burned at Alexandria, and Plutarch says the fire destroyed the great library, yet the Museum was still operating when Strabo described it, and Bagnall notes that blaming Caesar requires assuming the Library burned but the Museum did not. (2) Ammianus Marcellinus records that under Aurelian civil strife turned deadly and Alexandria lost the greater part of its Bruchion (palace) quarter; Bagnall reported in 2002 signs of a consensus that Aurelian's recapture of the city from the Palmyrenes (273, in his dating) was the occasion of the Palace Library's major destruction, though no ancient source mentions the Library in that episode. (3) The Serapeum, a temple complex that housed a library, was demolished in 391 under Theophilus, the Christian bishop of Alexandria, on an order from Emperor Theodosius I; the demolition is well documented, but Socrates Scholasticus's account does not mention books. (4) The story that Caliph Umar / Amr ibn al-As ordered the books burned in 642 first appears in 13th-century Arabic sources (Ibn al-Qifti) and is rejected by modern historians as a later fabrication. Modern accounts, such as a 2025 History.com explainer, describe a long decline punctuated by smaller fires and neglect rather than one dramatic event, though scholars differ on which episode did the most damage.