@MarilynG1, I appreciate your help, however when I changed that value to $0, it became clear to me that it's the wrong thing to do and $800 was correct after all.
That entry ends up on AZ Form 140, line 5C of Box 44C, which is the "Total charitable contributions made in 2021 for which you are claiming a credit under Arizona law..." The 5C amount is subtracted from the total charitable contributions so a 25% deduction can be given to contributions that DO NOT qualify for the credit. Setting the number to zero definitely causes double dipping on the AZ return because the $800 would get a 25% deduction AND a dollar-for-dollar credit (on line 51 which comes from Form 301).
