No.
It is not illegal for friends to give each other gifts. It is human nature to have extra antigens to give to friends in need.
It is against the law if an individual engages in selling antigens. Coronavirus detection reagents are managed as third-category medical devices. Individuals cannot engage in business activities of third-category medical devices and sell new coronavirus antigen reagents on online platforms such as Moments. The box is suspected of violating the law.