Why Can't Instantly I Claim My Winnings if the Market is Closed?

Answers are provided manually after the contract closes. This is because keeping the answer in the contract would mean everyone could see the answer. Everything will be in limbo and frozen until the contract owner reveals the answer. You can compare this answer's verification file with the verification hash later to make sure it is correct.

The market will look like this until the answer is revealed:

Once the answer is reveal, then the "Claim Winnings" button will appear.

How Do I Verify the Answer Hash Matches the Verification File?

A short time after the answer is uploaded , you the answer hash string will become a link to the verification file. You can then run the file through SHA256 to confirm the hashes match. The answer hash verification files could be audio, image, or text.

How Do I Verify My Selection in the Web 3.0 Popup?

You can click on the data tab of MetaMask, or view the data of the Tx you are sending with any other Web 3.0 provider. You can tell which answer you selected by the last digit in the string. Don't be concerned that you selection is off by one, it's not. This discrepancy is because arrays used in smart contracts start from 0, not 1 as we humans usually count.