For the self employment tax on the Schedule C Net Profit.
The SE tax includes what you already paid in from your W2s so your schedule SE tax will only be the difference up to the max amount of $8,853.60 for social security. The max income for social security for 2021 is $142,800 between W2 wages and the schedule C Net Profit. There is no max for the Medicare tax.
Schedule SE Line 7 is the prefilled max amount subject to Social Security Tax. If your total W2 and SE income is more than that you don't pay SS tax on the amount over $142,800. If your income is less then box 7 doesn't figure into it.
See the blank Schedule SE line 7
https://www.irs.gov/pub/irs-pdf/f1040sse.pdf
