SUMMARY *** The icons of the files displayed on the desktop and in Dolphin should match the icons of the default program that opened them *** STEPS TO REPRODUCE 1. 2. 3. OBSERVED RESULT EXPECTED RESULT SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: (available in About System) KDE Plasma Version: KDE Frameworks Version: Qt Version: ADDITIONAL INFORMATION
That's not how it works. The freedesktop mimetype spec (https://specifications.freedesktop.org/shared-mime-info-spec/shared-mime-info-spec-0.21.html) defines which icon is used for each file type. The icon is unrelated to the application associated with the file at a given moment in time. This allows consistent and meaningful icons even when no corresponding app is installed yet, when installing another app, when changing the associated app, etc. (See also the icon naming spec https://specifications.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html)