You are a non-resident alien for the first 5 calendar years or part-years of your F1 visa (from 2016 to 2020).
From 2021, you start using the Substantial Presence Test to determine whether you qualify as a resident alien.
Please see this IRS document on the Substantial Presence test:
https://www.irs.gov/individuals/international-taxpayers/substantial-presence-test
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