By the way, I have noticed that mostly people based in the USA are asking about COVID tests in IST.

As a reminder, if you are only traveling from the USA to Turkey & Turkey to the USA without any onward connection, the US CBP does not require a COVID test as a requirement for both entering the country and boarding the flight. Some states might have different rules but for the majority of the USA, you do not need a COVID test. If you are making one for your peace of comfort, that's up to you.

Obviously, if you're flying to a third country ( other than Turkey & the USA ), you might need a COVID test depending on the countries border requirements.