What is the ruling on resigning from a job if the manager is cheating and embezzling people's money, and what is the ruling on the salary received under these circumstances?

If the work is permissible and does not involve direct engagement in or assistance with what is unlawful, then the salary is lawful. However, one must advise those who cheat people, whether they are a manager or otherwise, based on the Prophet's (peace be upon him) saying: "Help your brother, whether he is an oppressor or oppressed," and "Whoever among you sees an evil, let him change it." But if the worker directly participates in cheating or assists in it, then he is a partner in sin, and he must desist from that, even if it means leaving the job, based on Allah's (the Most High) saying: "And do not cooperate in sin and aggression."