Schedule is incomplete or missing from your return. Complete the schedule with information that supports $3579on line 12 of from 1040. This is what the letter said.

[mesquitebean]

More information is needed for someone to comment.  I'll ask some questions folks will need to know to assist you.

Form 1040, Line 12 is "Standard deduction or itemized deductions (from Schedule A.)"

Did you manually choose to have TurboTax use itemized deductions instead of your standard deduction?   If so, why?  Also, if you elected that option (such as married filing separately), is there not a Schedule A in your return?

What is your filing status?    Single, married filing joint, married filing separately, head of household?

ADDENDUM NOTE 1/01/2024 at 11:25 PM Pacific: 

For another possibility, also see the information that  @ VolvoGirl left you in her comment below if you were a dependent.

@ jamerson herr 

[VolvoGirl]

1040 line 12 is the Standard Deduction or your itemized deductions.   Since the amount is less than the Standard Deduction you must be filing as a dependent or as Married Filing Separately?  It's strange the IRS  should be asking about line 12.

How much is your earned income on line 1 Wages?

The Standard Deduction for an individual for whom an exemption can be claimed on another person's tax return is limited to the greater of:

…..$1,250 or

…..Your earned income for the year + $400 (but not more than 13,850)

So you would get a minimum of $1,250 to a max of 13,850.

See Table 8 Standard Deduction worksheet for Dependents on page 26
https://www.irs.gov/pub/irs-pdf/p501.pdf

[fanfare]

The Schedule that is missing is Schedule A.

It is required if you do not take the standard deduction.

@jamerson herr