@TheeDuelist yes, when chess engines actually play the game they use opening books. Otherwise they'd select the same moves every time (if processing time doesn't vary).
I meant running a chess engine evaluation on the starting position of chess. Engines can then scan the game tree very deeply and judge evaluations for resulting positions, and for all engines there are moves that give white a slight advantage at the start. This is how engines changed how humans play chess openings, not because engines use opening books, but because they can evaluate the game tree better than us.
A forced win for black would mean the starting position's correct evaluation is -Infinity (or mate in X moves). Even if today's engines can't solve chess, a winning forced sequence for black will at some point result in a negative evaluation, no matter where you are in the game tree. So to believe "black has forced win in chess" means that if we just can run the engines for longer and deeper, the evaluation will at some point turn negative.