Your social security benefit may increase if you keep working (depends on your previous and future earnings record) but, in any case, employment taxes are mandatory for any earned income.
You have to
pay self-employment taxes on self-employment income even if you have already
have sufficient credits to qualified for (or
are even already receiving) Social Security benefits.
https://faq.ssa.gov/link/portal/34011/34019/article/3739/what-happens-if-i-work-and-get-social-secur...