Depending on the payment gateway, the amount of information available in the Order Transaction data could vary a lot.

For the PayPal gateway specifically, the transaction ID can be found under transactions > receipt > transaction_id subfield:

In EZ Exporter, you can use the formula below in the Calculated Fields to pull out the transaction_id from the transaction data and place it in a separate column in the CSV/Excel file:

",".join([i.receipt.transaction_id for i in load_json_data({{ transactions.successful_transactions }})])