Link to an article on this.
Also - did a quick google search For example, in 2021, a single filer with taxable income of $100,000 will pay $18,021 in tax. What this means for your "EV Credit" is that you have a liability of $18,021, thus you could collect on the full $7,500 tax credit and your liability would decrease from $18,021 to $10,521. It doesn't matter how much money you had withheld from your paycheck or paid in estimated taxes.
Now, there are people who do everything imaginable to not have declared income (paid under the table, barter, etc), that sort of thing. They may "earn" 100,000, but because they were paid under the table on most of their earnings (say a waiter working a minimum wage job and NOT declaring tips) they would have only declared 25,000 to the government and had $75,000 in undeclared income (exaggerating, I know....but still) Then.... you make $25,000 a year you will be taxed $2,106.
In that case, you will only get $2106 of the 7500 tax credit. The remaining ~5400 goes bye bye.