I was ED of a nonprofit which went out of business in 5/2020. I was paid for only one month in 2020 (for which I received a W2, but when we settled our finances, I was given the remaining money in our bank account, but no W2. How do I report this additional income?
I would enter as a substitute W2. Form 4852 is a substitute for Form W-2 that taxpayers can complete if they haven't received a W-2.
When you use TurboTax, we'll ask you a few questions to estimate your total wages and withholding using your final pay stub, and fill out Form 4852 based on your answers. The IRS doesn't allow Form 4852 to be filed electronically, so you'll need to print out the necessary forms and mail them to the IRS.
It might take the IRS longer than normal to process your return while it verifies your information. If you don't mind waiting, you can request an extension. This gives you additional months to get your W-2 and file a return.
Excerpt from What To Do If You Haven't Received a W-2 - TurboTax Tax
Does that mean I will have two W2s on this tax form, or do I report the untaxed amount on the W2 that I have and increase the amount of taxes owed?
It needs to be two separate entries. The W2 you actually have needs to match with your TurboTax W2 entries.
The other option to enter the additional income which should still allow you to e-file your return is to use the "Miscellaneous Income" section to report income that should have been on a W2 but wasn't.