Englisch vermeidet die Passivform, wann immer möglich.

hätte erlernt werden können = could have been learned best

Furthermore, it would have been expected that this complex structure could be learnt (recognized) best by the neural network

Moreover it would have been expected that this complex structure could have been learnt best from the neuronal network.

Thanks; you're all incredible people.

Question to Jo UK: Is my information nonsense? So for each of my translations into the passive mode has been changed into the active form by native speakers.

Werner, I'm not sure what other people have said about your translations. In this sort of scientific text, sentences in passive form would be as common as they ever are in English, so I guess we didn't see any obstacle to a literal translation. I hadn't seen the other suggestions, incidentally, so I had no opportunity to benefit from them.

@Jo UK, but it should be "learnt by" not "learnt from", I think, as the neural network is learning not teaching.

Yes, offliner, you're right, my sentence went off-track at the end, when I thought the hard work had been done.