How do you include a 1099-NEC that isn't in one of the categories?

It depends.  Assuming you are working for the same employer it should have been included in the W-2.  

It is subject to income tax and employment tax withholding, because it is compensation for work performed, even though the work will be performed in the future.   There is a way to handle this in TurboTax, using either form SS-8 or a substitute W-2 form, depending on when the bonus was paid.  If the bonus was paid in 2024 and the employee started work in 2024 and received a W-2, then use Form 8919 with code H.   Or if you have a W-2 from this employer, see instructions for Form 4852 below.

Form 8919:

Complete the steps (entered below for your convenience). The IRS will go back to your employer for their share.  

1. Scroll to Less Common Income
2. Start next to Miscellaneous Income 
3. Start next Other income not already reported on a form W-2 or Form 1099
4. Yes to did you receive any other wages
5. Continue through to Did you earn any other wages? and answer Yes
6. Select Employee compensation that was not reported on a W-2
7. Continue > Report your wages, employer information and select reason code H

This will report your wages and you will also see the information for the SS-8 along the way. You will pay only the employee share of social security and medicare taxes. Form 8919 will be included with your return, see the link below.

• What if Form 8919: Uncollected Social Security and Medicare Tax on Wages?

The Form SS-8 helps to differentiate between an employee and an independent contractor (self-employed).

Form 4852:

You can file as though you received a W-2, but may have to file by mail if you do not have the employer identification number (EIN) of your employer (should be on the 1099-NEC). In this case, complete a W-2 and then on the follow-up pages look for the page titled 'Do any of these uncommon situations apply to this W-2?'  

1. Select "Substitute form - I didn't get a W-2 from my employer and need to complete a substitute form."  
2. This will take you through the steps to complete the Form 4852 so you can file your return.