My 2019 2.7GhZ Quad Core Intel i7 MacBook Pro (16GB RAM) also was having the same issue. Under System Report, RAW Support for Z8 was not visible. I too spoke to Apple Support in SG and they were very helpful and were able to resolve the issue. The solution was as follows.
1. If you have imported RAW files from your Z8 into Photos before the Mac OS Sonoma 14.2.1 update was released, to delete them from Photos and shut down the application.
2, Next we updated my MacBook Pro to the Sonoma 14.3.1 update.
3. Even after updating it still did not show Z8 RAW Support in the Systems Report.
4. Then we launched Photos and re-imported the Z8 RAW files into Photos. Now the thumb nails were visible as normal in Photos, instead of the blank white rectangles I was seeing earlier.
5. Once the import was completed we checked the System Report once again and voila... Z8 appeared into RAW Support.
The apple support guy said that this issue was also seen when Z9 RAW support was added a year ago.