My source of income changed by a few dollars from 2020 to 2021. why would my fed refund more then double for 2021?

[JamesG1]

It is possible to report exactly the same income from one year to the next and the refund / balance due would change because:

• Federal tax withholding increased or decreased after a change of jobs or a change of payroll companies at the same job.
• Income is subject to capital gains treatment instead of ordinary tax rates.
• No longer qualifying or newly qualifying for a tax credit or deduction.
• The age or income of a dependent affects a tax credit or deduction.
• Qualifying under a different filing status.
• Qualifying / not qualifying for a Recovery Rebate Credit.

[SweetieJean]

Look at your 2020 and 2021 returns side by side.  Something may stand out.  Also check for any data entry errors, especially commas and decimal points.