VoNR means "Voice over New Radio" - and is a technology that allows for voice calls to be made over 5G networks without needing to switch back to 4G for the duration of the call.
VoNR is part of the evolution towards 5G networks being able to exist without relying on 4G for some functions - and is similar to how "Voice Over LTE" (VoLTE) was part of the evolution from 3G to 4G networks.