when is the phrase 'according to you' used correctly and what are its different contexts ? Can it replace ' in your opinion'?
According to X means 'as stated by X
In my opinion, Jane Austen is a great writer. (NOT According to me…)
According to you or, in your opinion.
"According to you" sounds very combative, where "in your opinion" is less so.
"According to you, x is true?" sounds like the speaker is arguing that x is not true, and they are mocking someone for claiming it is.
"In your opinion, x is true?" sounds like the speaker is simply asking for someone's opinion and not indicating whether they might agree with it. This could still be combative if the speaker is trying to trick someone into admitting an opinion (in order to disagree), but it could be simply inquiring. "In your opinion, should we use the blue or the green paint?" is in most contexts an honest request for advice.
Both of these phrases can be used as entire statements. If a doubtful claim is made, "According to you" as a rebuttal means that the claim is made only with the doubtful expertise and/or honesty of the one who made the claim. "In your opinion" is a far politer statement that the claim made is just an opinion. It may be meant as direct contradiction or to establish the possibility of debate, depending on context.