There has been a major change in terms of UE identities in 5G Networks compared to previous generations.
This is mainly attributed to native support for interworking with non-GPP networks however it also supports backward compatibility for 3GPP-related identities for previous generations.
IMSI has a new equivalent in 5G named SUPI.
SUPI is not sent on air in the clear-text and is concealed using some public key provided by the home network and the concealed version is called SUCI.
Also, there are a few changes in QoS implementation and we moved from Bearer-based (EBI) implementation to QoS Flow-based (QFI) implementation where it is possible to map Multiple RB (UE to gNB) to a single N3 tunnel (gNB and UPF) and also to map Multiple QoS flow to single RB using a new protocol layer introduced in 5G named as SDAP.
QCI in 5G is now called 5QI - 5G QoS Identifier.