I early exercised stock options in a startup in 2016 via 83(b). The company shut down last year. How do I report the loss in turbo tax without 1099B or 3921?

You need to enter that as an investment sale in TurboTax, by listing the sales proceeds as $0 and the cost basis as what you paid for the shares. If any income was reported as taxable to you on your W-2 form, you need to add that to whatever other money you paid to come up with a basis of shares sold.

You enter an investment sale in TurboTax as follows:

1. Investment Income
2. Stock, Mutual Funds, Bonds, Other
3. Indicate that you didn't receive a form 1099-B
4. Enter the sales in summary form
5. Enter the proceeds, cost basis and holding period

There is no way to "Indicate that you didn't receive a form 1099-B" currently in TurboTax. Two tax experts have tried different ways to do that in live help with screen share. Every attempts goes back to a screen that requires entering from 1099-B form.

When you attempt to enter an investment sale, you should see this screen that asks if you received a form 1099-B, to which you can answer "No":

I have called three different tax experts using live help. The screen you mentioned is no longer accessible. They tried different ways to get to the screen but failed. I have tried using other browsers and other computers.

I have the same problem. Could someone from Intuit please advise?

The page shown by ThomasM125 is part of the Investment Sale experience in TurboTax for Desktop only.

In TurboTax Online, you may enter your investment sale information "as if" you received Form 1099-B. Enter by Sales Summary and choose the appropriate "uncovered" option for sales type, since it was not reported to the IRS.

Sales proceeds would be $0 with a cost basis equal to what you paid for the shares. If any income was reported as taxable to you on your W-2 form, you need to add that to whatever other money you paid to determine the total basis of shares sold.

Thank you. Also, what if the dissolution actually happened in 2020, but I didn't file the capital loss last year? Can I still file for 2021?

@AnnPH9654  No. Unfortunately, for stocks that become worthless the "sale" must be entered at the time that you discover that they have become worthless.  If the dissolution of the company occurred in a prior year you will have to amend that prior year return and enter the sale there.  If you are amending your 2020 return then you should do that prior to completing your 2021 return because it may generate a capital loss carryforward for use on your 2021 return.