since you are not itemizing you can ignore this unless you have a state return where you take itemized deductions
what is meant by IRS instructions
if you paid 2020 real estate taxes in 2020 and you were itemizing you would reduce the amount you paid by this amount
or
if you paid 2020 real estate taxes in 2019 and took itemized deductions for that year then you need to report as income some or all of the credit.
