Hi there, @furbeasts2. Currently, the option to delete a primary vehicle is unavailable in QuickBooks Self-Employed (QBSE).
This is because the system requires at least one active vehicle to support the Mileage tracker feature.
Hence, the option to mark a Vehicle no longer in use will only appear for non-primary vehicles. Please see the screenshots for your reference:

For now, you can keep the current vehicle as is. If you purchase or add a new vehicle in the future, you can update your account by setting the new one as primary.
Once you do that, you'll be able to mark the original vehicle as inactive or no longer in use.
Please leave a reply below if you have further questions. I'll be here to help.