Taxable income may be computed differently between 2019 and 2020 depending on what was included in the return each year.
If your filing status changed or if you are no longer a dependent, taxable income could be impacted.
If you are experiencing different results for the amount of tax, check how much was withheld for 2020, what income or unemployment changes there were between 2019 and 2020, and consider which credits, if any, changed from 2019 to 2020.