Turbo Tax, annoyingly , does not allow attachments. So if using form 4797 for mark to market reporting of trades, you need to attach a list of the actual trades if you want to comply with that reporting requirement, Has anyone filed electronically and send those in separately by mail, or maybe there's a better way I don't know about to get the information uploaded.
I use Turbo Tax. You download all you trading transactions directly, into Schedule D. Turbo Tax does all the computation as to your tax liability if any. You look for your broker from the Turbo Tax list and enter your user name and password as when you login to your trading account. You will be asked by Turbo Tax which tax documents you need downloaded. Dividend and Interest Income from your broker account downloaded as well.
You need to log into your brokerage account from within TurboTax while doing your taxes. Your brokerage should have had the data ready by end of February. I know it may be uncomfortable to let TurboTax access your brokerage account because there have always been doubts about what they are doing with the data from your account besides just for taxes...you gotta do it. After you file your taxes...change your password to be safe. If you need further guidance...contact their support team. He may have filed electronically for an extension. wrbtrader