Is money earned from a contract to build a building considered unlawful (haram) if the contract includes a condition to install television channels containing prohibited content, while the rest of the project does not involve any prohibited elements?

A Muslim must be wary of anything that spreads evil and vice, and cooperation in sin and aggression is forbidden, as Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." It is not permissible to assist in disobedience, and whoever assists in it becomes a partner in sin. The ruling on installing mixed channels depends on your knowledge of the person for whom they are installed. If you know that they will only use what is permissible from them, then there is no harm. Otherwise, it is not permissible to install them or assist in doing so, for anything that leads to the forbidden is forbidden, and means take the rulings of their ends. The money earned from this work is not entirely forbidden. The forbidden portion of it must be disposed of by spending it on charitable causes with the intention of disposal, not charity.