Is it obligatory to return the entire stolen amount to the uncle, or is there a possibility that part of it belongs to the state or other people due to the nature of his work, which would necessitate a different course of action?

You must repent to Allah for what has happened, because seizing the property of Muslims is forbidden. Repentance is not complete except by returning the money to its owner or seeking his forgiveness. It is recommended to frequently recite the reported supplications for settling debt, such as: "O Allah, suffice me with Your lawful against Your unlawful, and enrich me with Your grace beyond anyone else." And the supplication: "O Allah, Lord of the seven heavens... settle our debts and enrich us from poverty." And the supplication: "O Allah, Possessor of sovereignty... have mercy on me, a mercy by which You make me independent of the mercy of anyone else." You should think well of your paternal uncle and not accuse him of taking what is not his, for the basic principle regarding what is in a Muslim's possession is that it belongs to him.