I made an excess Roth IRA contribution because my MAGI is too high, and the docs say there's a 6% penalty, but the "IRA Contribution Results" page is using 12%. Why?

Can you please clarify where you are seeing the 12%?

The penalty on an excess Roth IRA contribution is 6% of the the smaller of the excess Roth IRA contribution or the value of your Roth IRAs on December 31, 2023 (including 2023 contributions made in 2024). This is calculated on Form 5329 part IV.

Please see What happens if I made an excess Roth IRA contribution for additional information.