"no application was created for running file-to-app on plugin=packagekit with dedupe-flags=7 with file=/home/julien/Téléchargements/thunderbird.tmp/pcloud, elapsed time since creation 1ms"
Did you download the appimage of pcloud, then right-click on the file and select "properties" and then enable "Executable as program"? After that you can doubleclick on the file to launch it and sign in.