What is the ruling on a master's degree obtained by concealing one's employee status to bypass the "no objection" requirement, and working with it, and the money earned from it? And what is the ruling on money received as a grant for non-employee students, along with signing a pledge not to receive a salary from the state? And what is the way to repent and return this money?

You were obligated to adhere to the Ministry's condition, as Muslims are bound by their stipulations. You are not entitled to the amount disbursed by the Ministry to those who do not receive any salary from the state, and it is not permissible to take it. It must be returned by any convenient means, even by transferring the amount without informing them of the true situation. If that is not possible, or if it is highly probable that those in charge of the Ministry would not hesitate to take the money for themselves or misuse it, then give it as charity to the poor and needy or use it for public welfare. As for the certificate and working with it and the money resulting therefrom, if you passed the exams and are competent for the job, then the money resulting from that is lawful.