When I Installed WSL by default it installed Debian 10 which was the latest version available that time.
Not latest version of Debian bullseye released.
Method 1: Fails
Try to execute
sudo apt-get update && sudo apt-get upgrade && sudo apt-get dist-upgrade
sudo apt update -y && sudo apt full-upgrade -y
Method 2: Working Method confirmed in 2022
Open sources.list file and change every buster to bullseye
sudo vim /etc/apt/sources.list
to
This above version is the modified sources.list to update the debian to bullseye Debian 11 version.
Then execute following command:
sudo apt full-upgrade
Make sure to run
sudo apt update -y && sudo apt upgrade -y
Then Close and reopen the Terminal/Powershell/Bash window
Check your debian version now
Thats it.