Thank you for the quick response that seems to have moved me forward quite a lot. Sadly it still doesn’t work.
My project had an asset catalogue containing the old icon files (called images.xcassets) that I deleted. I created a new one, with the default name and inserted it at the top level of my project. I was then able to import the icon file that I called IconFile. That name is consistent with the name in Project > General; I did not tick “Include all icon assets”.
This didn’t work, even after a restart the old icon was still displayed. I then found that the icon file entry in my …-info.plist file still referred to the old icon (that I had removed) so I changed that to AppIcon.icon. That didn’t work either.
I cleaned the build folder, the app still runs but has a blank icon (being the outline containing the glass template in white on a pale grey background).
Assets.xcassets contains one item being the AppIcon. This is displayed as its three layers plus icon.json that references these and looks credible as the icon file.
Any pointers on where to go next would be greatly appreciated. I haven’t seen any diagnostics that seem relevant except a message that I think is long-standing at build time: “cannot open file at line 51040 of [f0ca7bba1c]” - I don’t see enough information there to follow it up.
Observation: The page you pointed me to in Xcode Help does not appear when searching on “icon”. Presumably why I didn’t find it.
Observation: the process described for creating an asset catalogue is out of date in https://developer.apple.com/documentation/xcode/managing-assets-with-asset-catalogs.
