Download the AppImage from https://ultimaker.com/software/ultimaker-cura and copy it to /opt
Extract the AppImage
/opt/Ultimaker_Cura-4.8.0.AppImage --appimage-extract
Get the icon cp squashfs-root/usr/share/icons/hicolor/64x64/apps/cura-icon.png /opt/Ultimaker_Cura-4.8.0.png