Thanks for all the explanations. I am wondering if Bb4 instead of Bf8 also win a piece directly?
You are right. Bb4 is a good move and would win easily after 35.Qc7 Rd3 36.Qb8+ Bf8
Once noticing that white has absolutely no defense, black can save calculation time (if in time trouble for example) by playing Bf8 to stop absolutely all threats including checks and threats against the bishop. There are many winning plans for black, so it is largely a matter of personal preference. I just wanted to point out that whites pieces are paralyzed in defense of each other and helpless against the threat of Rd3.
