What is the ruling on the salary of an engineer, knowing that his contractor obtains projects through bribery and orders the theft of raw materials, coupled with a scarcity of job opportunities and a fear of leaving this work?

If your work does not involve deception or assisting in a forbidden act, then the work is permissible (halal (definition)) and you are not obligated to leave it. However, it is preferable to leave it and seek another job if you have enjoined good upon your employer and forbidden evil, and he has not responded. But if your work requires you to participate in or assist in forbidden acts, then it is not permissible for you to remain in it, except in a case of necessity.