While most of the newer Android devices come with new technologies like VoLTE (Voice over LTE) and VoWiFi, older devices do lack these feature due to hardware limitations.
But some older devices are compatible with these new features and manufacturers do push these features to their devices via new OTA updates. Many Samsung devices have already received the VoLTE feature with a software update.
Now it looks like the unlocked variant of Samsung Galaxy Note 10+ on AT&T network has started receiving a new update which brings the feature to the device. Some users have reported this on Reddit.