The unemployment benefits that you received are community income. You are supposed to report half of it as your income and half of it as your wife's income. Each of you can exclude up to $10,200 of your individual half of the unemployment. TurboTax might now be doing this automatically, but did not do it when you originally filed your 2020 tax return.
As you correctly guessed, the IRS changed how the unemployment exclusion was calculated in a community property state. This is undoubtedly why they sent you an additional refund. Your IRS transcript reflects your tax return as originally filed. They do not update the transcript if they make a change.
See Q4 at the following link on the IRS web site.
2020 Unemployment Compensation Exclusion FAQs — Topic A: Eligibility
