What is the ruling on conducting some financial transactions at work, such as lending to employees without the manager's knowledge, or taking an advance from the fund, or dealing with loan interest, or handling deficits or surpluses in the fund, and is taking money and then returning it considered a breach of trust?

It is not permissible for you to dispose of the fund's money except with permission, because it is a trust. Disposing of it without the knowledge of the official is a betrayal, and the money taken is unlawful. You must repent and return what you have taken.

Paying usurious loans or deducting interest is unlawful, and you must refrain from it. If you cannot refrain from it, then you must leave your job.