I have a MacOS app which has its own documents. The documents are supposed to have custom icons, so that they are easily identifiable on -- e.g. -- the Desktop. They used to be visible, but they aren't now. In more detail ...
I have been upgrading and old app that was last built (in Objective C, using Xcode) under MacOS 10.13 (High Sierra). I have gotten the upgrade to build and run under Big Sur (still Objective C and Xcode).
Both the old and the new versions of the app successfully write usable documents. The documents created by both the old and the new app do show up on the Desktop with the correct icons when I copy the documents to an old Mac running High Sierra. They also show when I copy them to a Mac running Mojave. (I don't happen to have a Catalina partition handy, so I can't say about Catalina.) The exact same documents do not show up with the correct icons when I copy them to a newer Mac running Big Sur -- they show up with generic document icons. I have both the old and the new versions of the app installed on all these machines, so the Finder can do whatever it does to both versions to find out about document icons.
Obviously (I think), something has changed about how the Finder gets information about document icons, between Mojave and Big Sur, or possibly between Catalina and Big Sur. Does anyone know what it is? In particular, are there some new key/value pairs I should add to my Info.plist or to the Custom macOS Application Properties panel in Xcode, to make my custom document icons show up?
