you make mistake in writing it, the original is correct. remember such grammar rule as : If the adverb "only" produce or introduce an adverbial clause, the main verb should be in inversion. For example, Only in this way can you learn English well = You can learn English well only in this way. pay careful attention to : The "you can learn" is changed into → "can you learn". If there is not a modal verb "can" , you will use the "do" to replace it . → Only in this way do you learn English well = You learn English well only in this way.

In this context, the sentence is not a question. It’s a statement. In fact, it’s an inspirational statement. It’s telling you that only after misfortune can you appreciate the good things in life. If you added a question mark, you would either be asking what the sentence means or if it’s true. Example: Person 1: Only in the darkness, can you see the stars. Person 2: Only in the darkness can you see the stars? What does that mean? Are you sure that’s true?

The original is correct. When you use “only + preposition” for rhetorical effect, the subject (you) and auxiliary (can) are inverted. So, “Only in the darkness, can you see the stars.” (You can only see the stars in the darkness.) As far as I understand, your sentence “only in the darkness you can see the stars” would be incorrect in American English.

Both are correct. The first version is, perhaps, more old fashioned.