Reading this was so confusing. Referring to one person as "They", "Their" etc. This example is found in the help section on Underpayment Penalty.
"Example: In 2020, Lee paid $6,000 total in taxes. They changed jobs and thinks their income will be lower in 2021, so they plan to pay $5,000 in estimated tax payments for 2021.
When Lee prepares their..."