Excuse me, when taking landscape portraits, do people have to be in one third instead of the middle?

It should be said that it is recommended in this position, because it is close to the golden section, so the composition will feel better. You have every reason (even no reason) not to do so. I saw a photo in the textbook of the New York Institute of Photography, where two children were sitting at both ends of the springboard back to back. This photo destroyed almost all common sense, but it is still an excellent work.

Rules are meant to be broken!