By far the most common cause of this on a joint return is that you entered both your W-2 and your spouse's W-2 as if they were for the same person, instead of one for you and one for your spouse. When you first start to enter a W-2 in a joint return, you have to indicate whose W-2 it is. Entering both W-2s for the same person makes it look like that person had excess Social Security tax withheld, when there was actually no excess.
Did either of you have more than one employer? If you each had only one W-2, it's virtually certain that you did not have excess Social Security tax withheld, but you entered the W-2s incorrectly. If one of you had two or more W-2s, look at your W-2s - not in TurboTax - the actual W-2 forms from your employers. Add up the Social Security tax in box 4 of the W-2s for one person. Is it more than the maximum for the year in question? If not, you did not have excess Social Security tax withheld, and the IRS is right.
What year is the IRS notice for? The maximum Social Security tax for 2020 is $8,537.40. For 2019 it's $8,239.80. For 2018 it's $7,960.80.
