All the unsupported Catalina Mac are already whitelisted, I mean there is nothing to add for unsupported Mac, it's only for supported Mac 2012-2015 that are blacklisted from apple, but it's not only this, however from your pictures I guess I understood why Sidecar shows blackscreen, for two main reasons:
- You need an USB 3.0 XHCI bus, maybe using a PCI-Express USB 3.0 hub or some thunderbolt to USB 3.0 (or usb-type-C adapter); (This is the main issue)
- You may need a better Metal GPU (maybe the GT730) since your GT710 clearly doesn't support the "AirPlay Display Video Mirroring" from your "Cinema HD" picture (it should be as this example picture: https://cdn.tutsplus.com/mac/uploads/2013/07/airplay-syspref.jpg)
AirPlay Mirroring is old naming now they call it AirPlay Display
another example: https://forums.macrumors.com/thread...rking.2184104/page-7#lg=post-27578149&slide=0
And again having a dualGPUs system doesn't help, especially if one GPU is Metal and another is non-Metal, for example in a supported 2012 Catalina Mac dualGPUs either intelHD4000 and Nvidia GT 650M are both Metal.
Has anyone with a MacPro 5,1 and a GTX680 checked to see if they have mirroring in the display system preference panel?