I would be nice if Reallusion would update the ExPlus_Remap file, but their support says they won't be doing that. : (
Anyway, For the body I don't believe the RL_LLF_AnimBP is needed with 5.4. The CC4 Skeleton should work with the newer retargeting tools pretty easily.
For ARkit remapping this is what I've done so far, but I still have some testing to do. But I believe it's what the older BP does.
Create a Blueprint Class and under "All Classes" search for "LiveLinkRemapAsset" & open it.
Hold the mouse over the word Functions and a dropdown appears, select GetRemapped Curve Name.
Break the link between the Get & Return nodes.
Right click and add a "Switch on Name" node and add 52 (0-051) pins to it.
In the details panel for that node rename each pin with an ARKit shape. (
(Link to ARKit names https://developer.apple.com/documentation/arkit/arfaceanchor/blendshapelocation))
Then duplicate the "Return Node", one for every new pin. In their value boxes add the name of the CC4 shape that corresponds to the ARKit name and connect it.
Connect the out of the "Get Remapped Curve" node to the "Switch on Name" node, compile and save.
One the Character, create an Anim BP with the CC4 SKM.
Open it and add a LL Pose node select the iPhone and in the details panel set the "Retarget Asset" drop down to this new BP. Compile and save
I believe they shapes will then be retargeted from the iPhone to the CC4 character.