When we talk about facts or general statements we always use plurals. Human is countable, so humans. I like dog, not 'I like a dog'

There's a missing word in this sentence that a native speaker hears even though it isn't there: "Those robots can walk like humans WALK". You can say "human", but as a noun it requires an article like "a" or "the": "Those robots can walk like a human (walks)" "Those robots can walk like the human (walks)" "Those robots can walk like the humans (walk)"