CFBundleIconFile in misc/Info.plist was set to qelectrotech.icns, including the file extension.
Per Apple convention this key should hold the icon name without the extension — macOS appends .icns itself.
On recent macOS versions this mismatch causes the Finder to fall back to the generic placeholder icon instead of the actual app icon.
Fix: CFBundleIconFile → qelectrotech (no extension), matching the existing CFBundleTypeIconFile entries (elmt, titleblock, qet) which were already correct.
Laurent Trinques