It apparently didn’t help you

Let’s break this down so it’s easy to understand.
That stimulus check was an advance payment of the recovery rebate. If you didn’t receive that advance payment but are eligible, you could then claim it on your taxes. Following so far? Good.
It’s a refund (a “refundable tax credit”) that exists outside of your earned income for the year. This means you do not include it in your income, and you not pay taxes on it. It’s a fixed, absolute amount given back to you if you’re eligible. If you’re eligible for $2800 for example, you’re getting $2800 applied after all of your taxes are calculated. Need an example? Sure, let’s do a few.
Person A: Was eligible for $1400, received it via a stimulus check earlier in the year, does not impact his taxes.
Person B: Didn’t receive a stimulus payment, but is eligible for $1400. Does taxes and when finished, he
is owed $600. Recovery rebate applies at the end, and he receives $2000 back.
Person C: Didn’t receive a stimulus payment, but is eligible for $1400. Does taxes and when finished,
he owes the govt $400 in taxes. Recovery rebate applies at the end, and he receives $1000 back where he would have owed $400 otherwise.
If you do your taxes and discover that you shouldn’t have received the payment at all, guess what? You don’t have to pay it back per federal regulation.
This isn’t “free money” at all. It’s
your money that the the govt is handing back to you that you’ve paid with previous taxes. The stimulus payment and recovery rebate are the exact same thing. The only difference is when you ended up receiving it.
There is absolutely zero downside to it for you as a taxpayer, unless your stance is “Nah bro, it’s cool you want to give me back some tax money I paid you before, but I’d rather you keep it.”
If that’s your stance, feel free to give the govt all the donations you want. I’d personally take back all of my tax money I’d paid that they wanted to give me if I was eligible.
Child tax credits do have some variance, but that’s a different ballgame.