Command line instructions
The Flatpak app is included as part of the desktop bundle. Make sure the desktop bundle is installed before installing a Flatpak app: sudo swupd bundle-list | grep desktop
To install the desktop bundle, enter: sudo swupd bundle-add desktop
To add this Flatpak app, enter: flatpak install flathub cc.arduino.arduinoide
To run this Flatpak app, enter: flatpak run cc.arduino.arduinoide
For additional Flatpak commands, enter: flatpak --help