Created attachment 158422 [details] screenshot SUMMARY Download kolourpaint-23.04.0-1862-macos-clang-x86_64.dmg and try to open heif. The dialog does not have such supported format.
kolourpaint uses the Qt and KDE libraries to open files. It does not provide code itself for the image file formats. It seems Qt has still no support for this: https://bugreports.qt.io/browse/QTBUG-69212
Thanks!