What is the ruling on working as a civil engineer in a company that belongs to a bank dealing with usurious loans, knowing that the nature of the work is engineering and not financial?

Your brother is not permitted to work for a company affiliated with a usurious bank, even in an engineering supervisory capacity. This is due to the involvement in assisting in sin and transgression, aiding the bank in usury, strengthening it, endorsing it, and consenting to it. Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." And whoever fears Allah - He will make for him a way out and will provide for him from where he does not expect.