Missing Dock in Ubuntu 20.04 after sudo apt upgrade and restart

I did sudo apt upgrade and restarted Ubuntu 20.04 system. However, after login the Dock is missing from the desktop environment. The Dock does appear on the left edge of the monitor when I press the Super button to enter the Activities screen.

I have tried solutions 1 and also doing

$ sudo apt install gnome-shell-extension-ubuntu-dock
$ sudo dpkg-reconfigure gnome-shell-extension-ubuntu-dock

Each time reboot to check the appearance of the dock. Still missing.

noticed something strange in Settings --> Appearance --> Dock. Icon size is 0 and can't be changed and Show on is blank. Position on screen was initially blank. I could selected any of the options but Dock still does not appear. See image

Quite sometime ago, I had installed Dash-to-Dock and uninstalled it. Dock still appears and worked well for weeks until this upgrade. According to apt log, the affected packages were:

Upgrade: brave-browser:amd64 (1.27.111, 1.28.106), libegl1-mesa-dev:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), libegl-mesa0:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), update-notifier-common:amd64 (3.192.30.8, 3.192.30.9), libwbclient0:amd64 (2:4.11.6+dfsg-0ubuntu1.9, 2:4.11.6+dfsg-0ubuntu1.10), grub-common:amd64 (2.04-1ubuntu26.12, 2.04-1ubuntu26.13), libglapi-mesa:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), libglapi-mesa:i386 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), libxatracker2:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), grub2-common:amd64 (2.04-1ubuntu26.12, 2.04-1ubuntu26.13), grub-pc:amd64 (2.04-1ubuntu26.12, 2.04-1ubuntu26.13), libgbm1:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), samba-libs:amd64 (2:4.11.6+dfsg-0ubuntu1.9, 2:4.11.6+dfsg-0ubuntu1.10), grub-pc-bin:amd64 (2.04-1ubuntu26.12, 2.04-1ubuntu26.13), firefox-locale-en:amd64 (91.0+build2-0ubuntu0.20.04.1, 91.0.1+build1-0ubuntu0.20.04.1), libgles2-mesa-dev:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), distro-info-data:amd64 (0.43ubuntu1.5, 0.43ubuntu1.6), libgl1-mesa-dev:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), libgl1-mesa-dri:i386 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), libgl1-mesa-dri:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), libsmbclient:amd64 (2:4.11.6+dfsg-0ubuntu1.9, 2:4.11.6+dfsg-0ubuntu1.10), shim-signed:amd64 (1.40.6+15.4-0ubuntu7, 1.40.7+15.4-0ubuntu9), libgl1-mesa-glx:i386 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), firefox:amd64 (91.0+build2-0ubuntu0.20.04.1, 91.0.1+build1-0ubuntu0.20.04.1), mesa-vdpau-drivers:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), mesa-vulkan-drivers:i386 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), mesa-vulkan-drivers:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), update-notifier:amd64 (3.192.30.8, 3.192.30.9), mesa-va-drivers:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), libglx-mesa0:amd64 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1), libglx-mesa0:i386 (21.0.3-0ubuntu0.2~20.04.1, 21.0.3-0ubuntu0.3~20.04.1)
End-Date: 2021-08-20  06:44:43

How do I get the Dock to reappear?

Update

@vanadium I can't enable Ubuntu Docks from Extension or Tweaks. See below. Can't do your step 4.

Solution 1:

1. First, install the Extensions tool (gnome-shell-extension-prefs), load it up and disable the "Ubuntu Dock" extension if it is not already disabled.
2. Reset the configuration settings of Ubuntu Dock to the factory defaults with the following terminal command: dconf reset -f /org/gnome/shell/extensions/dash-to-dock/
3. (Likely not needed, but to make sure: log out then back in)
4. Reenable Ubuntu Dock in the "Extensions" tool. If you do not see Ubuntu Dock in the tool, try restarting first.

This will reset your personal dock configurations. An issue with the current configuration is most likely causing the problems. Ubuntu Dock is derived from the Dash to Dock extension, and shares the same configuration settings.

If problems persist, then there may be an issue at the system level. Then attempt a reinstall of the dock:

1. Remove with the command sudo apt purge gnome-shell-extension-ubuntu-dock. This will likely also remove the ubuntu-desktop metapackage. Likely not needed, but you could reboot now to be sure.
2. Reinstall ubuntu-desktop: sudo apt install ubuntu-desktop. This will pull Ubuntu Dock back in
3. If the event ubuntu-dock does not appear in the desktop environment, restart the system.