Puzzles good or bad?

I did a good movement and was a ́ ́mistake ́ ́ or ́ ́blunder ́ ́ . After i see with stoksfish was a good movement . I like more the puzzles of lichess some years ago . lichess.org/training/af1kJ 15..Kf4 is ́ ́bad ́ ́

Well, Kf7 is the only move that keeps Black's advantage. Nf4 (Knight=N) looks good, but White can play Qb5+ and after a series of precise moves White gets the piece back. Not an easy puzzle. SF14+ NNUE shows Kf7 as the only (good) move, not sure why you think Nf4 would also be good for Black.

Yeah, the old puzzles had you always winning material or finding checkmate, whereas the newer ones have some ambiguous solutions where you make some moves to maintain your better position, but the material might still be equal. I think the main advantage of the new puzzles is that they include end games where you need to promote, which were mostly absent before. When the puzzles got updated, the URLs for the old puzzles got changed as well, so I don't know of an easy way to identify them.