It appears that once USDT is sent to a smart contract address on Polygon without a withdrawal function, it is typically not possible to retrieve the funds. Smart contracts operate based on their predefined code, and if there is no functionality to recover or send the funds elsewhere, they might be permanently lost.

To potentially recover the funds, one could try to contact the developer of the smart contract. If you have the contract address, tools like Etherscan (for Ethereum) or Polygonscan (for Polygon) might provide information on the contract's developer or other contact details. However, success is not guaranteed, as it largely depends on how the contract was created and the intentions of the owner or developer.