Imitating non-Muslims in clothing that is unique to their religion is forbidden, such as dressing like a nun. Since a necktie is not connected to Christianity and is not exclusive to non-Muslims, it is fine to wear it.
Some claim that the necktie is connected to Christianity because you make a cross when tying it, but this is not true. The Romans were the first to wear knotted kerchiefs around their neck. Later, the modern necktie evolved from a cravat which originated in the 1600s where Croatian mercenaries wore it as part of their military uniform. It is important to fact-check things.
Shaykh Mustafa Umar