Very few manufacturers have sent out Android Oreo updates. Similarly, the few that have sent the updates have sent out for Android 8.0, not Android 8.1. This gives the Note 4 a better ranking among many devices not only at its price point but also worldwide.
If you haven’t received notification, check Settings – About Phone – System Updates.
If your update hasn’t arrived, be patient, keep checking. The size of the update is around 1.6GB so make sure you have enough data (or better yet use WiFi). Also, make sure your phone has enough internal memory space.