I found a solution and it involved reinstalling Docker entirely. Do note that you'll lose most of your settings by doing this.
sudo apt purge docker.io (removes Docker)
sudo apt autoremove (remove its other dependencies)
sudo apt install docker.io (installs Docker)
I got a little lost because I don't know if you mean Raspbian as "the original boot", but I don't think my confusion matters that much.
Since you apparently have not done much with your very-new installation, I would recommend you simply download a new Mate for Pi image from the ubuntu-mate web site, re-image the SD card, and then enjoy your new ...
It turns out Ubuntu 20.04 ARM64 already supports KVM acceleration on Raspberry Pi 4.
This is how I checked:
It appears the the w1-gpio, w1-therm and wire are in the generic kernel not the raspi I've not managed to build the kernel the instructions on line don't work. But at least I know that the drivers are available I just have not been able to build them.
I've recently downloaded and tried the 21.04 release candidate and that fully supports raspi One-Wire ...
Yes this one got me as well its because of the following parameter and its default settings;-
lock_passwd: Optional. Disable password login. Default: true
So the fix is to set lock_passwd: false in your 'users' section as the default is to lock the password by prefixing a '!'
There is no desktop rescue mode in Linux.
In a regular Debian or Ubuntu you instead have to start the rescue mode from the GRUB menu.
However, the Raspberry Pi installations don't use GRUB by default. So the other option is to boot on an install disk (i.e. a USB thumb drive) and use the rescue menu option from there.
There are plenty of posts about how to ...
Though the Pi is an ARM processor Ubuntu have classed these boards as IOT devices and have a specific build for them that can be found here
I would download this first then use the software to create the SD card image.
Edit: A list of supported ARM boards is here