The twist bones you generate when building the UE5 skeleton have a strange inconsistency given how closely the rest of the skeleton matches to native unreal. In the unreal skeleton, there are 2 twist bones for each limb segment (upper arm, lower arm, thigh, calf) but the 2 twist bones are "leaf" bones not "parent-child" bones as they are in the CC5 export. That is, the second twist bone is a child of the limb ("upperarm_r") rather than a child of upperarm_twist_01_r for example.

There is also an unfortunate naming inconsistency. All the other bones rename to match unreal but the twist bones (and the facial bones) are prefixed "cc_base_" with a name stem of "r_upperarmtwist01" instead of "upperarm_twist_01_r".

If you generate a game res version of the skeleton, there is only a single twist bone generated but it appears as though the naming is at least consistent with the unreal skeleton (upperarm_twist_01_r).

While I'm sure your tools/pipeline automatically handle the generated skeleton as you have it built, for workflows that involve other DCC tools (like MotionBuilder) or offline processing of skeleton data, it would really be a significant benefit to generate exported UE5 skeletons that match the twist bone hierarchy precisely. The naming convention is less significant but it also could not hurt to add consistency here since you're already doing it in in the game res skeleton.