I’m trying to reverse engineer something I could use some extra eyes.
If you have Big Sur installed, dig into the Contacts.app package. Its Assets.car file has both the new Big Sur style icon and the older version in the same file. If you take that app to a machine running Catalina, you will see the older icon. The app is disabled of course, but the older icon works. In the assets catalog, the old icon is named ‘Contacts’ and the new icon is named ‘Contacts-1016’. I’ve tried doing that, but haven’t had luck yet. I also noticed some apps have both the the CFBundleIconFile (that Xojo uses) and the CFBundleIconName Info.plist keys. I tried adding CFBundleIconName to my Info.plist, but it didn’t help.
My asset catalog has an App and App-1016 icon, since Xojo generates its app icons named App. Both my CFBundleIconName and CFBundleIconFile are set to App.
Any other ideas? This works somehow, I just haven’t found the right piece of the puzzle.