Sorry it is 2 different things. SS is taxed on ALL your income for the whole year. Nothing special for the first year SS. The only special first year rule is for your actual SS monthly checks won't be reduced.
First year special rule
https://faq.ssa.gov/en-US/Topic/article/KA-01927?msclkid=11bc282ccf2211ecb65078152b05ae6b
It doesn't say anything about the tax on it.
And See page 5 for the special first year rule
https://www.ssa.gov/pubs/EN-05-10069.pdf
