If working in banks is prohibited, is it obligatory to leave it to non-Muslims, even though all companies deposit their money in them and disburse salaries from them? And if a portion of bank interest enters the companies' money, how can one leave working in banks, knowing that banks now operate in investment fields and projects and do not rely solely on lending and borrowing?

Working in usurious banks is forbidden. The specious argument of "leaving them for non-Muslims" is refuted by the fact that a Muslim is commanded to avoid dealing with Riba (usury). Furthermore, this specious argument opens the door to legitimizing other forbidden acts. As for companies paying salaries from usurious, borrowed funds, this does not harm the employees as long as their work is permissible, and the sin falls upon those in charge of the company. The validity of banks not relying solely on lending does not change the ruling, because their investment projects depend on usurious funds, and the employee cannot distinguish between what involves Riba and what does not, so the matter remains based on the original prohibition.