Progress made! Since it seemed like it was a version-issue, I have tried to install other older versions. Your information that older version were still available by simple changing the url was very helpful with this. These were the results:
3.5.1: QHY worked
3.5.4: QHY worked
3.5.5: QHY crashed
3.5.7b: QHY crashed
Both cases that had the crashes were showing the identical messages of a version issue with libusb-1.0.0.dylib in the device manager.
So the good news, we're closing in on the issue and I now have a fully working KStars, albeit it being 3.5.4.
Would this give you some clues of what could go wrong with 3.5.5/3.5.7b, either in general, or the DMG image? And most importantly: how to correct it?
So I think what likely happened is that I had more than one version of the Libusb dylib on my Mac when I was building the last DMG and maybe QHY linked to a different one than the one that got packaged up. I will see what I can do about it.
Yep, I just confirmed it, the libqhyccd dylib is linked to my home-brew libusb which apparently is a different version number than the one in craft. One easy way to fix that is to delete libusb from home-brew and rebuild the dmg. Then all it would see is the one in craft.
Ok I made some changes to the recipes and some updates to the versions of some packages. I also managed to correct the version number issue so it says 3.5.6 stable since it isn't supposed to say 3.5.7 beta. I fixed it by downloading the stable zip file instead of the latest version. The most important thing is that I changed the version of libusb so that the one I have in home-brew matches the one in the craft folder, so that it doesn't matter which one it builds against. This should no longer have the QHY crash issue. Please verify that this build works better.
Great news! QHY Camera connects flawlessly! Thank you so much for your continued support Rob, to help finding the root cause of this issue and make the fixes. Much appreciated. Also nice to see the proper version number, to prevent confusion in the future when there might actually be a 3.5.7beta release.