lichess.org/training/61101Solution move: Qxc5Looks quite trivial and could be removed in my opinion.
lichess.org/training/61137first black move should be Qc5.
Don't forget there are pure beginners also on this site. You will get puzzles matched to your puzzle rating so this won't bother you.
61137: Qc5 b4! wins for white. But I agree Qc5 is more challenging response.
yes, that is the idea. It is more difficult to find in my opinion, even if that black move may not be the best answer.
I've find in many puzzles that comp doesn't reply with the most challenging move but I guess it is hard to implement. Constructing an algorithm for what's difficult to spot by human eye.