Voilà ce que j'ai fait.
Le log de la dernière :
jarodd@ubuntu$ flatpak install flathub com.valvesoftware.Steam Required runtime for com.valvesoftware.Steam/x86_64/stable (runtime/org.freedesktop.Platform/x86_64/18.08) found in remote flathub
Do you want to install it? [y/n]: y
Installing in system:
org.freedesktop.Platform/x86_64/18.08 flathub a7738ded72d8
org.freedesktop.Platform.Locale/x86_64/18.08 flathub 2e2113c42338
org.freedesktop.Platform.VAAPI.Intel/x86_64/18.08 flathub ff6f5fd65d8f
org.freedesktop.Platform.html5-codecs/x86_64/18.08 flathub dfcf5ab1cbd4
com.valvesoftware.Steam/x86_64/stable flathub 5a28acecb14a
permissions: ipc, network, pulseaudio, wayland, x11, devices, devel, multiarch
file access: xdg-music:ro, xdg-pictures:ro
dbus access: org.gnome.SettingsDaemon, org.gnome.SettingsDaemon.MediaKeys, org.kde.StatusNotifierWatcher
system dbus access: org.freedesktop.NetworkManager, org.freedesktop.UPower
tags: proprietary
org.freedesktop.Platform.Compat.i386/x86_64/18.08 flathub f3840e4632ee
Is this ok [y/n]: y
Installing: org.freedesktop.Platform/x86_64/18.08 from flathub
[####################] 774 metadata, 12529 content objects fetched; 243018 KiB t
Now at a7738ded72d8.
Installing: org.freedesktop.Platform.Locale/x86_64/18.08 from flathub
[####################] 33 metadata, 154 content objects fetched; 4464 KiB transf
Now at 2e2113c42338.
Installing: org.freedesktop.Platform.VAAPI.Intel/x86_64/18.08 from flathub
[####################] 3 metadata, 2 content objects fetched; 1761 KiB transferr
Now at ff6f5fd65d8f.
Installing: org.freedesktop.Platform.html5-codecs/x86_64/18.08 from flathub
[####################] 2 metadata, 1 content objects fetched; 833 B transferred
Now at dfcf5ab1cbd4.
Installing: com.valvesoftware.Steam/x86_64/stable from flathub
[####################] 47 metadata, 66 content objects fetched; 5641 KiB transfe
Now at 5a28acecb14a.
Installing: org.freedesktop.Platform.Compat.i386/x86_64/18.08 from flathub
[####################] 63 metadata, 1103 content objects fetched; 136971 KiB tra
Now at f3840e4632ee.
jarodd@ubuntu:~$
Donc ça semble bien installé (pas d'erreur en tout cas. Mais Steam ne se lance pas.
Sinon, je trouve tout cela bien compliqué. Il m'a fallu installer snap pour installer VLC, maintenant flatpak pour installer Steam. Alors qu'avant, un simple .deb suffisait...