The IRS agent was wrong. You only use your earned income. Maybe the amendment didn't 'see' that you had elected to use your 2019 Earned income? Your 2019 earned income was higher than it was in 2021, right?
While not directly saying you only use your income, the law itself implies it. It say that if you file a Joint return, you would add your earned income to your spouse's earned income. That effectively means if you don't file a Joint return, you only use your earned income.
