Unity is not working properly since 2021-06-15 system updates

[AO]

On Ubuntu Impish.
Since the system was updated 2021-06-15, Unity is not loading properly, if at all:
Lightdm is not working anymore, the system loads to a black screen with a cursor. Gdm3 does work and is able to load the Unity session.
Once in Unity, I’m greeted by an error message instead of the regular Ubuntu background:
“Something went wrong.
An error occurred and the system can’t load.
Log out and try again.
‘Close session’ button.”
Using the Alt+launcher number, I am sometimes able to start an app, and after several, Unity may load, launcher and all, but the error message stays in the background.

The environment theming and icons have all changed and Unity Tweak Tool can’t switch them back. GTK may be involved.
Some features have been lost:
I can’t start the calculator from the keyboard shortcut, number lock is not enabled on start up
Settings > Power doesn’t return any energy readings.
I can’t put the system to sleep. If I hit Fn+F8 on my keyboard, the session kinda resets and most (all) my apps are killed.
Upon first loading the sessions, there is no cursor. If I manage to load and access Nemo, then the cursor appears with a big X, and eventually shows an arrow.
Etc.

Here are the packages that were dist-upgraded between 2021-06-15 and 2021-06-17:

Commit Log for Thu Jun 17 15:30:00 2021
The following packages were updated:
google-chrome-stable (91.0.4472.106-1) to 91.0.4472.114-1
libplymouth5 (0.9.5-0ubuntu3) to 0.9.5-0ubuntu3.1
plymouth (0.9.5-0ubuntu3) to 0.9.5-0ubuntu3.1
plymouth-label (0.9.5-0ubuntu3) to 0.9.5-0ubuntu3.1
plymouth-theme-spinner (0.9.5-0ubuntu3) to 0.9.5-0ubuntu3.1
plymouth-theme-ubuntu-logo (0.9.5-0ubuntu3) to 0.9.5-0ubuntu3.1
plymouth-theme-ubuntu-text (0.9.5-0ubuntu3) to 0.9.5-0ubuntu3.1

Commit Log for Thu Jun 17 13:53:57 2021
The following packages were updated:
evince (40.1-1) to 40.2-1
evince-common (40.1-1) to 40.2-1
gnome-shell-extension-appindicator (35-1) to 40-1
libevdocument3-4 (40.1-1) to 40.2-1
libevview3-3 (40.1-1) to 40.2-1
network-manager-gnome (1.18.0-1ubuntu2) to 1.22.0-0ubuntu1

Commit Log for Wed Jun 16 18:00:52 2021
The following packages were updated:
gir1.2-gtk-3.0 (3.24.25-1ubuntu6) to 3.24.29-1ubuntu1
gtk-update-icon-cache (3.24.25-1ubuntu6) to 3.24.29-1ubuntu1
libgail-3-0 (3.24.25-1ubuntu6) to 3.24.29-1ubuntu1
libgtk-3-0 (3.24.25-1ubuntu6) to 3.24.29-1ubuntu1
libgtk-3-bin (3.24.25-1ubuntu6) to 3.24.29-1ubuntu1
libgtk-3-common (3.24.25-1ubuntu6) to 3.24.29-1ubuntu1
lintian (2.104.0ubuntu2) to 2.104.0ubuntu3
ubuntu-advantage-tools (27.1~21.10.1) to 27.1~21.10.1.1

Commit Log for Wed Jun 16 14:01:26 2021
The following packages were updated:
libbpf0 (1:0.3-2ubuntu1) to 1:0.4.0-1ubuntu1
power-profiles-daemon (0.1-5) to 0.8.1-1

Commit Log for Wed Jun 16 08:04:52 2021
The following packages were updated:
distro-info-data (0.48) to 0.49

Commit Log for Tue Jun 15 18:18:26 2021
The following packages were updated:
gstreamer1.0-pipewire (0.3.27-1) to 0.3.28-1
iio-sensor-proxy (3.0-2) to 3.1-0ubuntu2
libpipewire-0.3-0 (0.3.27-1) to 0.3.28-1
libpipewire-0.3-common (0.3.27-1) to 0.3.28-1
libpipewire-0.3-modules (0.3.27-1) to 0.3.28-1
libspa-0.2-modules (0.3.27-1) to 0.3.28-1
pcmciautils (018-12build1) to 018-13
pipewire (0.3.27-1) to 0.3.28-1
pipewire-bin (0.3.27-1) to 0.3.28-1

The following packages were installed:
pipewire-media-session (0.3.28-1)

Commit Log for Tue Jun 15 13:07:23 2021
The following packages were updated:
libinput-bin (1.17.2-1) to 1.18.0-1
libinput10 (1.17.2-1) to 1.18.0-1
librygel-core-2.6-2 (0.40.0-1ubuntu1) to 0.40.1-1ubuntu1
librygel-db-2.6-2 (0.40.0-1ubuntu1) to 0.40.1-1ubuntu1
librygel-renderer-2.6-2 (0.40.0-1ubuntu1) to 0.40.1-1ubuntu1
librygel-server-2.6-2 (0.40.0-1ubuntu1) to 0.40.1-1ubuntu1
rygel (0.40.0-1ubuntu1) to 0.40.1-1ubuntu1

Commit Log for Tue Jun 15 11:02:47 2021
The following packages were updated:
dnsmasq-base (2.84-1ubuntu2.1) to 2.85-1ubuntu1
gdm3 (3.38.2.1-2ubuntu1) to 3.38.2.1-3ubuntu2
gir1.2-gdesktopenums-3.0 (3.38.0-1ubuntu1) to 40.0-1ubuntu1
gir1.2-gdm-1.0 (3.38.2.1-2ubuntu1) to 3.38.2.1-3ubuntu2
gnome-control-center (1:3.38.6-0ubuntu2) to 1:40.0-1ubuntu1
gnome-control-center-data (1:3.38.6-0ubuntu2) to 1:40.0-1ubuntu1
gnome-control-center-faces (1:3.38.6-0ubuntu2) to 1:40.0-1ubuntu1
gsettings-desktop-schemas (3.38.0-1ubuntu1) to 40.0-1ubuntu1
initramfs-tools (0.140ubuntu5) to 0.140ubuntu6
initramfs-tools-bin (0.140ubuntu5) to 0.140ubuntu6
initramfs-tools-core (0.140ubuntu5) to 0.140ubuntu6
ipp-usb (0.9.18-1ubuntu1) to 0.9.19-1ubuntu1
isc-dhcp-client (4.4.1-2.2ubuntu7) to 4.4.1-2.2ubuntu8
isc-dhcp-common (4.4.1-2.2ubuntu7) to 4.4.1-2.2ubuntu8
libgdm1 (3.38.2.1-2ubuntu1) to 3.38.2.1-3ubuntu2
libgupnp-1.2-0 (1.2.4-1ubuntu1) to 1.2.7-1
remmina (1.4.17+dfsg-1) to 1.4.18+dfsg-1
remmina-common (1.4.17+dfsg-1) to 1.4.18+dfsg-1
remmina-plugin-rdp (1.4.17+dfsg-1) to 1.4.18+dfsg-1
remmina-plugin-secret (1.4.17+dfsg-1) to 1.4.18+dfsg-1
remmina-plugin-vnc (1.4.17+dfsg-1) to 1.4.18+dfsg-1
ubuntu-settings (21.04.3) to 21.10.1

The following packages were installed:
zstd (1.4.8+dfsg-2.1)

Commit Log for Tue Jun 15 08:36:44 2021
The following packages were updated:
distro-info-data (0.47) to 0.48
libtspi1 (0.3.14+fixed1-1.1) to 0.3.14+fixed1-1.2
libv4l-0 (1.20.0-3) to 1.20.0-4
libv4lconvert0 (1.20.0-3) to 1.20.0-4

ProblemType: Bug
DistroRelease: Ubuntu 21.10
Package: unity 7.5.1+21.10.20210601.1-0ubuntu1
ProcVersionSignature: Ubuntu 5.11.0-20.21+21.10.1-generic 5.11.21
Uname: Linux 5.11.0-20-generic x86_64
.tmp.unity_support_test.0:

ApportVersion: 2.20.11-0ubuntu67
Architecture: amd64
BootLog: Error: [Errno 13] Permission non accordée: '/var/log/boot.log'
CasperMD5CheckResult: unknown
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity:Unity7:ubuntu
Date: Sat Jun 26 09:36:02 2021
DistUpgraded: Fresh install
DistroCodename: impish
DistroVariant: ubuntu
DkmsStatus: virtualbox, 6.1.22, 5.11.0-20-generic, x86_64: installed
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] Picasso [1002:15d8] (rev c9) (prog-if 00 [VGA controller])
   Subsystem: Advanced Micro Devices, Inc. [AMD/ATI] Picasso [1002:15d8]
InstallationDate: Installed on 2020-03-15 (467 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Alpha amd64 (20200106)
MachineType: To Be Filled By O.E.M. To Be Filled By O.E.M.
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.11.0-20-generic root=UUID=1f0c807d-38ab-4f08-807c-43b04774ca66 ro quiet splash vt.handoff=7
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 05/06/2021
dmi.bios.release: 5.17
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: P4.00
dmi.board.name: B450M Steel Legend
dmi.board.vendor: ASRock
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrP4.00:bd05/06/2021:br5.17:svnToBeFilledByO.E.M.:pnToBeFilledByO.E.M.:pvrToBeFilledByO.E.M.:rvnASRock:rnB450MSteelLegend:rvr:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.family: To Be Filled By O.E.M.
dmi.product.name: To Be Filled By O.E.M.
dmi.product.sku: To Be Filled By O.E.M.
dmi.product.version: To Be Filled By O.E.M.
dmi.sys.vendor: To Be Filled By O.E.M.
modified.conffile..etc.default.apport: [modified]
mtime.conffile..etc.default.apport: 2020-03-15T11:56:34.801446
version.compiz: compiz 1:0.9.14.1+21.10.20210501-0ubuntu1
version.libdrm2: libdrm2 2.4.105-3
version.libgl1-mesa-dri: libgl1-mesa-dri 21.1.2-1
version.libgl1-mesa-glx: libgl1-mesa-glx 21.1.2-1
version.xserver-xorg-core: xserver-xorg-core 2:1.20.11-1ubuntu1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:19.1.0-2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20200714-1ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.17-1

[AO (aofrl10n)]

According to Khurshid Alam, “this is due to an update of gsettings-desktop-schemas to 40. A fix is in progress. So you can either wait for the fix or downgrade gsettings-desktop-schemas meanwhile to 3.38 and it will work.”

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.