What is the ruling on teaching in schools that practice saluting the flag, chanting Ba'athist slogans, and gender mixing, and that include materials that violate Sharia and the theory of evolution?

The matters mentioned about the school are reprehensible acts that violate Islamic law. The salute to the flag is an alien custom that is not permissible. The Ba'ath Party holds deviant principles, and it is not permissible to educate students upon them. Darwin's theory contradicts the Qur'an. It is preferable to avoid working in this school. However, if you are not teaching these subjects, then this does not prevent you from working, and you must denounce the reprehensible acts as much as you are able. As for the forbidden mixing, if you are safe from the temptation of women and adhere to the Sharia-compliant regulations, then there is no harm for you in working.