Apple didn't break anything, let's not forget that by definition we are dealing with unsupported types.
I have similar issues as you, except me it works perfectly on the simulator, and not on my iphone 12, and I have been extensively trying out things.
But before being at that issue, I had other ones, including this on macOS, where a quicklook issue happened to a user that shortly after happened to me as well, and I could pinpoint what it was: I had installed an app right before encountering the issue, an app the user had as well, and that app changed the UTI of the file extension.
So for me, I just had to add that UTI to my extension's QLSupportedContentTypes.
I know that is not your issue, however it might provide insight: in order for the other app to 'hijack' the UTI, it actually used 'Imported type' and not 'exported type',
so you can try this instead?:
Additionally, checking your app's info.plist, I see you declare 'Fuji Compressed RAW Image' as having two UTIs. From my understanding, the way to do that is to declare it twice, with a single UTI each time.
Regarding the versions issues on macOS, do you understand loud and clear how QuickLook almost stubbornly looks for the extensions at the path it found it the first time? i.e. if you built and launched from /Applications, and then you build again and launch from /Derived-Datas, it's still going to fetch it from /Applications and if it has been deleted, it might get confused and act like there is no extension?
Also, if you need to debug the actual extension, what you have to do is run the extension's from Xcode, but not with 'QuickLookSimulator' but rather with "Finder', there you'll get the debug messages.
You might have to use osLog and set each variable to public in the string, if it comes out as private.
If you fixed your issue, please tell, that's where I am at right now