I missed grabbing the book my first playthrough and also went back to the silent library. For me, the book was along the right side bookshelves, after a succeeded perception check. If you've checked your inventory, all your companion's inventories, backpacks, camp storage and all the venders you sold books to, it seems your problem may be similar to the user whose bookshelf was broken/had acid spilt on it during the fight.
I hate to say it, but you need this book
to progress to the boss fight and end Act 2. I agree with the users who said to go back and redo the portion of Act 2 prior to going to the Gauntlet of Shar. I know, you said you have spent almost 200 hours in Act 2, and as someone who spent 247 hrs on her first playthrough alone, I can relate. I have 4 backpacks full of 100+ unique books each and I actually READ THE BOOKS. Disgusting. I know. In your head you tell yourself, I just can't do all of this over again, but it's really a mental constraint you put on yourself. The moment you stop telling yourself you can't and just put one foot in front of the other and just do it, I'm telling you, yes you can. You'll reach the same point in no time. There are dialogue options, characters, and things I never saw the first time. In my third playthrough, I actually had a fight and cutscene play, that NEVER HAPPENED in my previous runs.
I finished a second Dark Urge playthrough, and enjoyed it even more than the first. My thought is, rather than waiting, brooding and losing time waiting for Larian to fix this; take the matter into your own hands and try your best to work your way back to this point. If you're adamant about keeping this existing file, maybe consider making a brand new character so you can at least play and have fun while you wait. I swear you'll reach the same point in no time, and it's *so much faster* than you think.
