This implied for many “a virgin”. Sort of like the word “maiden” in English, implies that she might well still have a “maidenhead”/ hymen. But “virgin” is NOT a direct translation, especially in the context of that young woman giving birth.
Apostasy is a bit of a strong word for ‘walking back’ a incorrect translation to one that is more accurate, if less directly prophetic of the doctrine of perpetual virginity.
See my #27. Virgin is the proper translation as the Septugint would be a better source text than the 10th century masoretic text.