@ manu, j'ai fait comme tu m'as dit et revoilà le message d'erreur, (dans Muon par exemple, c'est le plus court) :
[ gpgv:/var/lib/apt/lists/partial/download.opensuse.org_repositories_graphics:_darktable:_master_xUbuntu%255f22.04_InRelease
The following signatures were invalid: EXPKEYSIG 040524A84C70D8B5 graphics:darktable OBS Project <graphics:darktable@build.opensuse.org> ]
[ gpgv:/var/lib/apt/lists/partial/download.opensuse.org_repositories_graphics:_darktable:_master_xUbuntu%255f22.04_InRelease
The following signatures were invalid: EXPKEYSIG 040524A84C70D8B5 graphics:darktable OBS Project <graphics:darktable@build.opensuse.org> ]
François-Marie