As far as I know, the Sidecar problem is not the result of the BCM94360NG module, but of the SMBIOS module that is chosen in your configuration. In my case, I have set the "MacPro7,1" profile because it is the most coherent with my uses, but Sidecar gets disabled because it relies on the iGPU, which is absent on the Mac Pro because it uses Xeon processors.
I believe that the "iMac18,3" and "iMac19,1" profiles should work with this build and enable Sidecar, but I have not tested them and you probably will encounter other problems/incompatibilities down the road, because some apps will think there is an iGPU while there is not. A classic example of this is QuickLook that usually tries to use the iGPU when it is supposed to exist considering the SMBIOS profile, which results in an empty window when displaying pictures.
Check out
this page for more information on this.