Ayn is pronounced “eyen”. At least everything I’ve seen and heard lately.
Who knows how it was pronounced? I think it’s unique even for Russians.
I remember clearly when I started reading it in the mid-60’s EVERYONE told me then is was “Ann”, not “Eyen”..............
And I have a degree in English Lit, but not Russian or American Lit.
Clearly the dominant argument today is “Ann”. I say, “Who knows for sure?”