Since you're married filing jointly, it sounds like you and your spouse qualify for the additional standard deduction amount for age and/or blindness. That accounts for the additional $2,600.
Your standard deduction for 2020 starts at $24,800. Then,
Add $1,300 if you were born before January 2, 1956.
Add $1,300 if your jointly-filing spouse was born before January 2, 1956.
Add $1,300 if you were blind as of December 31, 2020.
Add $1,300 if your jointly-filing spouse was blind as of December 31, 2020.
