@icakmak
(a) you entered the US originally in 2015 with F-1 and assuming that this was your first entry, you would have been an exempt person till 12/31/2019. From 2020 Jan 1st you start counting days present towards SPT.
(b) you left the country in July 2020 and so may ort may not have met the SPT.
(c) You re-entered the USA again on F-1 in 2021. This time however you are not an exempt status person because you have used up your original five year exempt status. And therefore must count your days present towards SPT.
(d) Because of this situation you probably became a resident for tax purposes in 2022. So you file return on form 1040 for 2022 and 2023 onwards.
(e) FICA exemption ( or not ) has nothing to do with exempt status. If you are a trainee / student working in your on campus or education related institution etc. then your are immune from FICA.
Suggest talk to your "employer" whether you are a trainee or an employee ( employees must pay FICA ).
Does this help ?
pk
