Since Roth contributions are made with after-tax money, they don't provide a tax deduction to lower your bill. The most likely reason your refund is dropping is that your income exceeds the 2025 eligibility limits, causing a 6% excise tax penalty for an "excess contribution." Essentially, if you earned too much to qualify for a Roth, the IRS charges you a fee for putting money into one.
Here are the Roth limits: Amount of Roth IRA contributions that you can make for 2024
