First, to give you the answer, in your position you need to exchange your knight for his, and after he takes back with his queen, attack his queen with your bishop, which seems to offers your bishop as a sacrifice, but it's poison for him.
I agree with you. I don't want to take anything away from the terrific amount of work that went into this, it's a great achievement... but it needs to have a richer set of choices for the learner, and it would be nice if it could explain more exactly what was wrong with each of your erroneous choices, and perhaps provide a more directed set of hints that laid out what you should be looking at by explaining weaknesses in the position or "obvious" signs of opportunity, rather than demanding a very specific single course of action. Why all the alternative moves are weaker is as useful as why the good moves work. What might work is if the site had a "wiki" style of notation adding, so a richer database of explanations could be crowdsourced.
Back to the problem, if it's of any help to you, I came up with the answer by noting that I need to move my knight out of the way to get my black bishop active and onto those juicy squares defended by my pawns, and to get my white bishop out of the way to open the file for my linked up queen and rook, and also that his queen is threatening my undefended pawn so I looked to get my bishop onto that diagonal as a defender.
This position is a good example of a number of core concepts, for example that the bishops because they are on diagonals coordinate a little better with the other pieces when they are on the flanks of the attack rather than in the middle where they can clog, and that the rooks and queen benefit from open files, and that knights are useful when the position is somewhat clogged but frequently they should be exchanged for a more advantageous opening of the position. But the pedagogy here does not teach that.
I am a decent (but very rusty) chess player, but what I am good at is a little more "holistic", I play by developing my position in more or less sensible ways and then exploiting opportunities when they arise; but a lot of that is somewhat unconcious thought learned from a great deal of play, and "understanding" my position for me comes from being the one who developed it. In contrast, it is hard for me to jump in and look at a developed position and find the magic in it which is what this style of teaching requires. Probably a good set of things for me to work on, but at the same time the chess rating it gives me is absurd because I play at a much higher level than 1200 but I have tremendous difficulty getting my score to climb. I mention this because even though you and I come at this from different places, my complaint about the site is the same as yours: it's demanding a very specific set of moves and it's not really explaining or guiding as much as it needs to. Sometimes I pick the right move and it says "congrats! let's move on" and I'm thinking I have no idea what was so great about what I chose, the move seemed sensible but not stunning.
Now, I may be not the typical user (as an experienced, highly intuitive player with voids where big chunks of my skills are lacking, so the system should not be redesigned for me) but I mention it because while I can rely on some of my developed talents to solve these problems, I don't feel that this would teach those talents that I do have, and they would be very useful for learners to develop.