Is it illegal to make idol dolls?

it's infringement, unless you have the right to portrait. But regular companies generally buy the right to portrait.

infringement, of course. Because as long as it is for profit, public sale not only violates the portrait right of the star, but also may infringe the copyright (works using the image, etc.) and other rights of some commercial companies. If it is not for profit, and it is not sold publicly, it is only for appreciation, and it does not constitute infringement.

Portrait right is the right that citizens can agree or disagree with others to use their portraits. The law stipulates that portraits of citizens shall not be used without their consent. Portraits and documentary photographs, if taken without the consent of the portrait owner, cannot be published or exhibited in principle, even if they are purely non-profit-making exhibitions.