I tried entering nothing, and I also entered a date in the future, and I also went back to the federal 'self-emplyed' business section (schedule C) of the software and looked everything over
Return to the Self-Employed section and review your entries for your vehicle. Look closely for a box that says "I stopped using this vehicle in 2021." If this box is checked, there must be a date in the box below. This would be the date you stopped using the vehicle for this business. This doesn't mean you sold it, just that you stopped using it.
I have the same issue for 2022. It wants a sell, given away or abandoned date for a vehicle I did not use for business in 2022. I still have the vehicle. I did not check the box that I stopped using the vehicle in 2022 because I might use it in 2023
If you're asked for a disposition date, you may have checked a box that indicated you sold the vehicle or answered another question that triggered a sale. Review your answers in the vehicle section carefully to confirm your entries.
If you've reported this vehicle using only the standard mileage rate in the past (no expenses or depreciation), you have the option to enter essentially no mileage for the year instead of reporting that you stopped using it. You do need to enter at least one mile in this section to avoid an input error.