Various examples and schemes pertaining to sidelink resource allocation for vehicle-to-everything (V2X) in New Radio (NR) mobile communications are described. An apparatus implemented in a first user equipment (UE) receives a first signaling from a network node of a wireless network, with the first signaling configuring a first sidelink resource for a sidelink between the first UE and a second UE. The apparatus transmits a packet or transport block (TB) to the second UE on the sidelink using the configured first sidelink resource. The apparatus also receives a second signaling from the network node responsive to the second UE failing to decode the packet or TB, with the second signaling dynamically configuring a second sidelink resource for the sidelink. The apparatus then retransmits the packet or TB to the second UE on the sidelink using the dynamically configured second sidelink resource.