Question: Upon T421 expiry, if a UE's (target) L2 U2N Relay UE changes its serving PCell to a different cell before indirect path addition/change, and MCG transmission is not suspended, what procedure should the UE initiate?
Option 1: Direct Path Establishment Procedure
Option 2: Indirect Path Failure Information Procedure
Option 3: Connection Reconfiguration Procedure
Option 4: Handover Preparation Procedure
Explanation: According to the specified behavior for T421 expiry and the scenario where the target L2 U2N Relay UE changes its serving PCell before the indirect path addition/change, if MCG transmission is not suspended, the UE should report the failure of the indirect path addition/change. This is specifically done through initiating the Indirect Path Failure Information Procedure, highlighting the importance of timely reporting of failures in maintaining efficient network operations and user experience in complex relay scenarios within 5G NR (New Radio) networks.