Should an employer be informed about previously taken money without his knowledge, or is it sufficient to return the money and repent, given that informing him will cause significant problems?

You have done well by repenting and returning the money to your workplace, as the Prophet, peace and blessings be upon him, said: "A hand is responsible for what it has taken until it returns it." You are not required to confess to the officials what you have done; rather, returning the money, even through indirect means, is sufficient. You have already returned the money and more, thereby absolving yourself. Do not inform the official about your transgression, for Allah has concealed it for you.