[MHGinTN]

A better rendering of The Apostasia is The Departure or the departing. Here is the Geneva Bible rendering:

3 Let no man deceive you by any means: for that day shall not come, except there come a departing first, and that that man of sin be disclosed, even the son of perdition.

The 'that day' in the Greek refers back to the day of the Lord. And the chapter begins by focusing the reader on the gathering unto Him that we should not be deceived over because the departure comes 'proton' / first before the man of sin who is the bane of the tribulation years can emerge.

The first several English translation Bible from the Greek rendered apostasi as only departure or departing.

[Jan_Sobieski]

Apostasia is “defection” or “to apostasize”. Never in the New Testament is it used for “Departing” or “leaving”. Look it up

[Jan_Sobieski]

I am trained in Greek. Your changing of the scripture is incorrect. Your change of the scripture changes the entire meaning of the verse…

3 Let no man deceive you by any means: for that day shall not come, except there come a apostasia (defection, apostasy) departing first, and that that man of sin be disclosed, even the son of perdition.

[ducttape45]

Pretty much every English Bible after the Geneva has rendered that scripture wrong. Everything from the Wycliffe Bible to the Geneva rendered it correctly, as you said, as “departing.”
Hard to believe to there are so many hard-headed folks who just can’t accept the truth in that passage.