I think the Whisper models will all use GPU. Only the Parakeet model is limited to CPU.

(I'm unfamiliar with AppImage. Was the model included in the app image, or was there a download after selecting the model?)

not sure this might help, but when you launch the .appimage in a terminal, it shows you the command to extract the files it contains (to speed the loading) ; this might help you find the files you're searching for, maybe :)