Comment 7 for bug 1880541

ubuntu@lp1880541-f:~$ dpkg -l udev|grep udev
ii udev 245.4-4ubuntu3 amd64 /dev/ and hotplug management daemon
ubuntu@lp1880541-f:~$ sudo groupadd kvm
groupadd: group 'kvm' already exists
ubuntu@lp1880541-f:~$ grep kvm /etc/group
kvm:x:108:
ubuntu@lp1880541-f:~$ sudo groupdel kvm
ubuntu@lp1880541-f:~$ grep kvm /etc/group
ubuntu@lp1880541-f:~$ sudo groupadd kvm
ubuntu@lp1880541-f:~$ grep kvm /etc/group
kvm:x:1001:

ubuntu@lp1880541-f:~$ sudo apt install udev
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  libudev1
The following packages will be upgraded:
  libudev1 udev
2 upgraded, 0 newly installed, 0 to remove and 31 not upgraded.
Need to get 1440 kB of archives.
After this operation, 2048 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:1 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 udev amd64 245.4-4ubuntu3.1 [1362 kB]
Get:2 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libudev1 amd64 245.4-4ubuntu3.1 [78.3 kB]
Fetched 1440 kB in 1s (1423 kB/s)
(Reading database ... 66302 files and directories currently installed.)
Preparing to unpack .../udev_245.4-4ubuntu3.1_amd64.deb ...
Unpacking udev (245.4-4ubuntu3.1) over (245.4-4ubuntu3) ...
Preparing to unpack .../libudev1_245.4-4ubuntu3.1_amd64.deb ...
Unpacking libudev1:amd64 (245.4-4ubuntu3.1) over (245.4-4ubuntu3) ...
Setting up libudev1:amd64 (245.4-4ubuntu3.1) ...
Setting up udev (245.4-4ubuntu3.1) ...
The group `kvm' already exists and is not a system group. Exiting.
dpkg: error processing package udev (--configure):
 installed udev package post-installation script subprocess returned error exit status 1
Processing triggers for systemd (245.4-4ubuntu3.1) ...
Processing triggers for man-db (2.9.1-1) ...
Processing triggers for libc-bin (2.31-0ubuntu9) ...
Errors were encountered while processing:
 udev
E: Sub-process /usr/bin/dpkg returned an error code (1)

(clear the error and downgrade udev again, and add -proposed to apt sources)

ubuntu@lp1880541-f:~$ dpkg -l udev|grep udev
ii udev 245.4-4ubuntu3 amd64 /dev/ and hotplug management daemon
ubuntu@lp1880541-f:~$ sudo groupadd kvm
groupadd: group 'kvm' already exists
ubuntu@lp1880541-f:~$ dpkg -l udev|grep udev
ii udev 245.4-4ubuntu3 amd64 /dev/ and hotplug management daemon
ubuntu@lp1880541-f:~$ grep kvm /etc/group
kvm:x:108:
ubuntu@lp1880541-f:~$ sudo groupdel kvm
ubuntu@lp1880541-f:~$ grep kvm /etc/group
ubuntu@lp1880541-f:~$ sudo groupadd kvm
ubuntu@lp1880541-f:~$ grep kvm /etc/group
kvm:x:1001:

ubuntu@lp1880541-f:~$ sudo apt install udev
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  libudev1
The following packages will be upgraded:
  libudev1 udev
2 upgraded, 0 newly installed, 0 to remove and 46 not upgraded.
Need to get 1442 kB of archives.
After this operation, 4096 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:1 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 udev amd64 245.4-4ubuntu3.2 [1363 kB]
Get:2 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 libudev1 amd64 245.4-4ubuntu3.2 [78.9 kB]
Fetched 1442 kB in 1s (1415 kB/s)
(Reading database ... 66302 files and directories currently installed.)
Preparing to unpack .../udev_245.4-4ubuntu3.2_amd64.deb ...
Unpacking udev (245.4-4ubuntu3.2) over (245.4-4ubuntu3) ...
Preparing to unpack .../libudev1_245.4-4ubuntu3.2_amd64.deb ...
Unpacking libudev1:amd64 (245.4-4ubuntu3.2) over (245.4-4ubuntu3) ...
Setting up libudev1:amd64 (245.4-4ubuntu3.2) ...
Setting up udev (245.4-4ubuntu3.2) ...
The group `kvm' already exists and is not a system group. Exiting.
update-initramfs: deferring update (trigger activated)
Processing triggers for systemd (245.4-4ubuntu3.1) ...
Processing triggers for man-db (2.9.1-1) ...
Processing triggers for libc-bin (2.31-0ubuntu9) ...
Processing triggers for initramfs-tools (0.136ubuntu6.2) ...
update-initramfs: Generating /boot/initrd.img-5.4.0-40-generic