What is the ruling on working as a supervisor of computer systems for accounts and purchases for people characterized by extravagance, squandering, and injustice in their dealings?

It is permissible to work in establishments that have lawful activities, even if unlawful things might be presented there, provided that the worker does not directly engage in the unlawful act and does not assist in it. If your work involves direct engagement in something unlawful or assisting in it, then it is unlawful. Extravagance varies according to the circumstances of individuals.