Is it permissible to work for the government of a non-Muslim ruler? What is the ruling on the guardianship of a disbeliever? And what is the ruling on a Muslim working in the army of a secular country?

The guardianship of a disbeliever over Muslims is not valid. As for working in governments headed by non-Muslims, as long as it does not involve aiding falsehood, participating in wrongdoing, or demeaning and humiliating a Muslim, there is no objection to it, because this falls under the category of commutative contracts.

As for working in secular armies, its ruling is derived from the concept of secularism which clashes with religion. It is forbidden to assist them except out of fear of their evil. However, if joining the army is for the purpose of reform and changing evil, with the consultation of people of knowledge, then there is no objection at that time.