Without comparing tax returns, we don't know exactly what changed. If you claimed a recovery rebate ($1400) because you did not get a round 3 stimulus, that would have been removed. You would lose the $500 credit for other dependent or up to $3000 child tax credit, depending on his age. You might have lost head of household status and reverted to single, which has higher tax rates overall.
The real question is whether your son can be independent. He must answer "yes I can be claimed as a dependent by someone else" if he can be claimed, even if he does not want to be claimed. If he answers "No, I can't be claimed as a dependent by someone else" when he actually can be, that might be tax fraud and financial aid fraud. If he can be claimed, you don't have to amend. The IRS will investigate and he will be forced to amend. Or, you can let it go and not raise a fuss, in which case you have to amend and pay the extra tax.
