How are v3 onion addresses more secure than v2 addresses?


I rarely use TOR, but I noticed sometime (I believe) last year, there was something about them switching from V2 addresses to V3 addresses, which were longer, and they gave onion sites some time to make the change. (This kinda screwed me because an online library where I happened to find some harder-to-find books never updated its address, and won’t load anymore.) From what I understand, the new V3 addresses are supposed to be more secure, but when I tried to find why, the explanations confused tf out of me. Something about the longer addresses being a key and the shorter ones the hash of a key, and other stuff I don’t get. Could someone make it simple for me?

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Care to share the library name?