to avoid penalty you need to have paid thru withholding or timely quarterly estimated taxes, either 100% of your 2023 tax liability, or 90% of your 2024 tax, whichever is smaller - the 'safe harbor' amount. See estimated tax FAQ for more info https://www.irs.gov/faqs/estimated-tax or the instructions for Form 2210.
If you are getting an underpayment penalty in 2024 then something may have changed just enough to miss the safe harbor. So I suggest to figure what the 'safe harbor' amount was for your situation in 2024 and see if withholding and estimated taxes were enough and that will likely explain the penalty.
If you are on TT desktop go to Forms, double click on the penalty on the 1040 then double click again on the worksheet and it will bring up Form 2210 which does this calculation. Not sure equivalent with TT Online but either way this form should also be in the PDF with all forms/worksheets.
You may also need to adjust withholding for 2025, you can work thru this under Other Tax Situations / Form W4 and Estimated Taxes.
