If you want legitimate, long-term protection, you have two safe options:
For the technically curious, why does 2038 appear so often in cracks and fake keys? Avast Free Antivirus Activation Code Till 2038
Even if such a key works initially, Avast’s licensing servers perform periodic health checks. The key will be flagged as invalid, downgrading you to the free version without warning. You lose your money and gain nothing. If you want legitimate, long-term protection, you have