According to IRS Instructions for Form 1040 or 1040-SR, on page 26:

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.

If your Form 1099-R shows a taxable amount, you can report that amount on line 5b. But you may be able to report a lower taxable amount by using the General Rule or the Simplified Method or if the exclusion for retired public safety officers, discussed next, applies.

You can also access those instructions in TaxAct, by clicking Form Instructions on the right.

Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.