Is it obligatory to disclose the secret of the accounts manager who mistakenly transferred company funds to my account twice, knowing that disclosing this secret could expose him to severe penalties, reaching imprisonment or dismissal and deportation?

The default is to assume the best of people, and what has been mentioned does not conclusively prove the manager's intent or malice. Rather, it is more likely that he made a mistake in the transfer. Therefore, it is advisable to cover for him, especially since the matter has passed and there is no proof of his betrayal, based on the Prophet's (peace be upon him) saying: "Whoever covers a Muslim, Allah will cover him on the Day of Resurrection." Returning the money to him so he can return it to the company's treasury is the correct action, and you bear no sin as long as you are not certain that he used it unlawfully.