The IRS has alerted us that there was an error in the printed instructions for form 1040/1040-SR. The error concerns which line numbers to copy from in using IRA Deduction Worksheet-Schedule 1, Line 19 (page 92 in the printed, January 6, 2021 version of the instruction book).
The current electronic version of the instruction book (February 9, 2021) has corrected the error, and Maxwell has paper copies of IRS Notice 1451 giving the correct instructions for those working from the paper instructions.