Social security only becomes taxable when added to sufficient other income.  If you are otherwise required to file a tax return, you do need to enter all your SS in Turbotax (TT). TT will determine the taxable portion, using the IRS work sheet. You don't enter a "percentage"

How much  is "sufficient other income"? The simple answer is $12,000 (a single person's filing requirement). But the answer varies dependent on marital status, filing status, age, the amount of your Social security.

In your case, none of your social security will be taxable.

The $13,600 standard deduction will reduce your income subject to income tax.  You will owe no income tax.

The $13,600 standard deduction will not reduce any of your Self employment Income subject to self employment tax (social security and medicare).