You can't claim anything until you receive a 1098-C from the qualified charity that you donated the car to. That 1098-C will have the value on it, that you are allowed to claim on your tax return. At best, you can only claim what Goodwill gets for the car when they sell it, or what they "expect" to get for it.
Depending on the condition of the car they may part it out and sell individual parts of the car. In that case the 1098-C would show the total amount received for all parts sold in that tax year. You can only claim what's on the 1098-C for whatever tax year that 1098-C is issued for.
It is not uncommon for someone who donates a car towards the end of the tax year (2019 for example) to not receive a 1098-C until the end of the next tax year. So it's perfectly possible you may donate the car in Dec of 2019, yet receive a 2020 form 1098-C in Jan of 2021.
