Is working in the design and printing of Christian agendas and publications, at the request of a Christian friend, considered celebrating Christian holidays, and thus is the earning from it permissible (halal) or forbidden (haram)?

The work of a Muslim in printing papers and publications related to the Christian holiday is not permissible, because it falls under the category of assisting them in their invalid religious holidays. Sheikh al-Islam Ibn Taymiyyah mentioned that it is not lawful for Muslims to imitate Christians in their holidays in anything specific to them, neither in food, nor clothing, nor anything else, nor to sell anything that assists them in that for its sake. Al-Dusuqi mentioned the dislike of selling food or other things, such as clothes, and renting animals and ships, etc., to a disbeliever for the sake of his holiday. Since this work is not permissible, the earnings from it are not permissible.