What is the ruling on working at a central bank that deals with usury after having worked at an Islamic bank, and is it permissible to return to it because of the benefits it offers?

It is not permissible to work in interest-based banks (riba-based banks) because it involves assisting in sin, and Allah has forbidden cooperation in sin and aggression. The justifications a person might mention for such work are from the embellishments of Satan. Therefore, a Muslim should not exchange Allah's covenant for a small price, for what is with Allah is better and more lasting.