Your tax liability is only indirectly related to your refund. Your tax liability is what you actually pay to the IRS net after all payments, credits and refunds. For example, if you paid $10,000 in withholding and estimated payments and got a $6000 refund, your tax liability was $4000. On the other hand, if you had $3000 in withholding and paid an extra $1000 with your tax return, that would also be a tax liability of $4000.
Your EV credit can't be more than your tax liability. The other answers told you where to find it on last year's return. You will have to determine whether this year is likely to be similar or different.
Note that if you are self-employed, your tax liability for the EV credit is only income tax. Self-employment tax is not included in the calculation of your income tax liability.
