Yes, you were exempt from 2016-2018. Years 2019 and 2020 do not apply since you were not in the US for that period of time. If you were in the US in yrs 2021-2022, those are the two remaining years you have left on your 5-yr lifetime exemption period.
For 2023 and 2024, you are not exempt thus you would need to pay your FICA taxes for those years because you met the substantial presence test starting in the year 2023 and became a resident alien.
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