As the Plus is 99.9% the same as the original 4, it’s probably down to something as simple as the USB product ID (PID) presumably being different for the Plus.
As they’ve already mapped the Prime 4, I’d suggest posting on the Algoriddim forum and requesting support. It may be as simple as adding the PID to the existing mapping, so the software recognises that it’s a Plus.
If you saw the Mojaxx video of him touring their offices, they have a lot of controllers, so maybe they just don’t have a 4+