(X11) Gtk cannot open display: :0 with dual monitor setup

Hi,

I did not find any thread about that ?
Well, I connect a monitor as a 2nd display to my laptop. When I try to launch a snap, I get:
Gtk cannot open display: :0
Tested with foliate or snap-store.
Sweet-home-3d is ok, though.

$ snap --version
snap    2.44.3+20.04
snapd   2.44.3+20.04
series  16
ubuntu  20.04
kernel  5.4.0-31-generic

$ snap list
Nom                     Version                     Révision  Suivi          Éditeur       Notes
core18                  20200427                    1754      latest/stable  canonical✓    base
core20                  20                          634       latest/stable  canonical✓    base
foliate                 2.1.1                       142       latest/stable  johnfactotum  -
gnome-3-28-1804         3.28.0-16-g27c9498.27c9498  116       latest/stable  canonical✓    -
gnome-3-34-1804         0+git.3009fc7               33        latest/stable  canonical✓    -
gtk-common-themes       0.1-36-gc75f853             1506      latest/stable  canonical✓    -
snap-store              3.36.0-78-ge29ea9a          445       latest/beta    canonical✓    -
snapd                   2.44.3                      7264      latest/stable  canonical✓    snapd
sweethome3d-homedesign  6.2                         9         latest/stable  jibel         -

Can you post the output from running the following command in a terminal, please?

snap connections snap-store

This will let us know if the interfaces have become confused.

$ snap connections snap-store
Interface                 Plug                                      Slot                             Notes
appstream-metadata        snap-store:appstream-metadata             :appstream-metadata              -
content[gnome-3-34-1804]  snap-store:gnome-3-34-1804                gnome-3-34-1804:gnome-3-34-1804  -
content[gtk-3-themes]     snap-store:gtk-3-themes                   gtk-common-themes:gtk-3-themes   -
content[icon-themes]      snap-store:icon-themes                    gtk-common-themes:icon-themes    -
content[sound-themes]     snap-store:sound-themes                   gtk-common-themes:sound-themes   -
dbus                      -                                         snap-store:packagekit-svc        -
dbus                      -                                         snap-store:snap-store            -
desktop                   snap-store:desktop                        :desktop                         -
desktop-legacy            snap-store:desktop-legacy                 :desktop-legacy                  -
fwupd                     snap-store:fwupd                          :fwupd                           -
gsettings                 snap-store:gsettings                      :gsettings                       -
network                   snap-store:network                        :network                         -
network-manager           snap-store:network-manager                -                                -
packagekit-control        snap-store:packagekit-control             :packagekit-control              -
password-manager-service  snap-store:password-manager-service       :password-manager-service        -
personal-files            snap-store:dot-snap-auth-json             -                                -
snapd-control             snap-store:snapd-control                  :snapd-control                   -
system-files              snap-store:hostfs-usr-share-applications  :system-files                    -
system-observe            snap-store:system-observe                 :system-observe                  -
upower-observe            snap-store:upower-observe                 :upower-observe                  -
wayland                   snap-store:wayland                        :wayland                         -
x11                       snap-store:x11                            :x11                             -