Though I am new to 5G network but based on my previous learning of LTE and study of 5G, I came to know that paging will be supported in 5G network as it is supported in LTE network. In 5G network, Session Management Function (SMF) and User Plane Function (UPF) both are responsible for data path. Once UE moves to CM-IDLE state, UPF can't forward the incoming downlink data.
In this case, either SMF or UPF supports buffering of downlink data, location of buffering is decided by SMF.
If buffering occurs at SMF, then it relays all the buffered data to UPF once UE moves to CM-CONNECTED state so that UPF forwards the same buffered data to NG-RAN and thereafter it continues to forward the incoming data to NG-RAN as usual it does.