The Apple Pro XDR Display only supports a USB-Type C input. The Decklink 12G offerings include SDI (and therefore HDMI) but don’t include USB-Type C output. I don’t know if BMD will offer a product that uses USB-C and can send the video/audio information in correct form.
You can connect the XDR to the computer running Resolve and produce HDR deliverables up to 1000 nits that will playback on the display but the XDR is not a guarantee that all colour values will be accurately shown. The principal complaint is that miniLED backlights affect the image which can suffer from a glow or ghosting around intense light against very dark areas. A future microLED XDR panel should correct that problem.
Apple purposefully made this display only usable in Final Cut Pro X. Even if Blackmagic were to make a device to connect to it, they would need Apple protocols for telling the monitor to change viewing mode, because the monitor settings cannot be changed without apple software.
In other words the monitors settings are tied directly to the MacOS.
You should still be able to use the monitor as a video clean feed, but I don't know how accurate that would be.