@Opus 17 - it is not 'taxable income' - that infers Line 15 after the standard deduction.
it's gross income , not including social security. See page 11 on the right:
https://www.irs.gov/pub/irs-pdf/p501.pdf
The person's gross income for the year must be less than $4,400
that is for 2022; for 2023 it's $4700
