If box 2a on the Form 1099-R is the same amount as in box 1 then on the Form 1040 Line 5a will be blank
IRS Form 1040 Instructions (2023) page 27 - https://www.irs.gov/pub/irs-pdf/i1040gi.pdf#page=27
If your pension or annuity is fully taxable, enter the total pension or annuity payments (from Form(s) 1099-R, box 1) on line 5b; don’t make an entry on line 5a
