Could be any number of reasons: changes in your filing status, dependents, income, deductions, credits, taxes withheld, etc.. The tax law also changed. Check your data entry for any typos, and then look at 2019 and 2020 side by side.
You are posting from TurboTax Live. You can arrange for the Live help you are paying the extra fee for with your questions from 5 a.m. to 9 p.m. Pacific time.