Did Cain repent ? Regardless of translation being promoted ... Well, that is between the Heavenly Father and Cain...
The unpardonable sin is a specific sin that only a few will ever be in a position to commit .. regardless of translation or some preacher/priests commentary. The unpardonable ‘sin’ is also a time signature yet to be fulfilled.
Did Cain repent
Can you have forgiveness of sin without repentance?
Can you have repentance and no forgiveness of sin?
My conclusion is that for the transaction to be complete you need both. Sometimes forgiveness comes before the repentance. There are many incomplete transactions.