To add to Jack Rawlins' answer, you can also disable the Ubuntu Dock extension without using the terminal with the Gnome Extensions app in Ubuntu 20.04. Go to the Extensions app, and flip the "Ubuntu Dock" switch to disable it. It should do the same as the command posted by Jack.
The below will disable the default ubuntu dock this should resolve the issue.
To add to Jack Rawlins' answer, you can also disable the Ubuntu Dock extension without using the terminal with the Gnome Extensions app in Ubuntu 20.04. Go to the Extensions app, and flip the "Ubuntu Dock" switch to disable it. It should do the same as the command posted by Jack.