Deferred Social Security Taxes

You probably did not defer anything.  Your employer was allowed to defer this tax.

Check the amounts in box 3 of your W-2 and the amount in box 4.  Box 4 should be 6.2% of Box 3. 

This does not affect your tax return, only your social security account. For most employees no action is required.

Review the IRS Notice 2020-65 which explains more about this topic.

To Employers: 

If you deferred the employee portion of Social Security tax under Notice 2020-65, when reporting total Social Security wages paid to an employee on Form W-2, Wage and Tax Statement, include any wages for which you deferred withholding and payment of employee Social Security tax in box 3 (Social security wages) and/or box 7 (Social security tips). However, do not include in box 4 (Social security tax withheld) any amount of deferred employee Social Security tax that has not been withheld.

To Employees:

If you had only one employer during 2020 and your Form W-2c, Corrected Wages and Tax Statement, for 2020 (if you get one later), only shows a correction to box 4 (or to box 14 for employees who pay RRTA tax) to account for employee Social Security (or Tier 1 RRTA tax) that was deferred in 2020 and withheld in 2021 pursuant to Notice 2020-65, no further steps are required.