No, you cannot make a donation in 2020 and use it on your 2019 tax return. If you want to use it on your 2019 tax return, you have to make the donation in 2019. And it might not have any effect on your tax due or refund anyhow, unless you will have enough other itemized deductions to exceed your standard deduction. With the increased standard deductions that began with 2018 tax returns, many people do not have enough itemized deductions to make a difference.
STANDARD DEDUCTION
Many taxpayers are surprised this year because their itemized deductions are not having the same effect as they did on past tax returns. The new higher standard deduction and the elimination of certain deductions, as well as the cap on state and local taxes have had a major impact.
Your itemized deductions have to be more than your standard deduction before you will see a change in your tax owed or tax refund. The deductions you enter do not necessarily count “dollar for dollar;” many of them are subject to meeting tough thresholds—medical expenses, for example, must meet a threshold that is pretty hard to reach. The software program uses all the IRS rules that apply to the expenses you enter, and it tells you if you have enough to use your itemized deductions or if using the standard deduction is more advantageous for you. Under the new tax laws, some deductions have been capped—there is a $10,000 limit to the itemized deductions for state, local, property and sales taxes.
2019 Standard Deduction Amounts
Single $12,200 (+ $16,50 65 or older)
Married Filing Separately $12,200 (+ $1650 if 65 or older)
Married Filing Jointly $24,400 (+ $1300 for each spouse 65 or older)
Head of Household $18,350 (+ $1650 for 65 or older)
DONATING A CAR
https://ttlc.intuit.com/questions/2565781-how-much-can-i-deduct-for-donating-a-car
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.