2020 Schedule SE line 7 $137,700 and Part II line 14 $5,640 are prefilled amounts. Line 7 is the 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 $137,700. If your income is less then box 7 doesn't figure into it.
See it's even on the blank IRS SE form
https://www.irs.gov/pub/irs-pdf/f1040sse.pdf
