Howto upgrade debian

update from 10 to 11

list all packages in hold status:

sudo apt-mark showhold 

if any packages appear in the list, remove the hold status for each package:

sudo apt-mark unhold [package_name]

upgrade all packages to the latest version:

sudo apt update && sudo apt upgrade -y

install the gcc-8-base package:

sudo apt install gcc-8-base -y

backup /etc/apt/sources.list file

cp /etc/apt/sources.list /etc/apt/sources.list.bk.$(date +%F)

update /etc/apt/sources.list file with bullseye repos:

cat > /etc/apt/sources.list << EOF
deb http://deb.debian.org/debian bullseye main contrib non-free
deb http://deb.debian.org/debian bullseye-updates main contrib non-free
deb http://security.debian.org/debian-security bullseye-security main
deb http://ftp.debian.org/debian bullseye-backports main contrib non-free
EOF

now upgrade your system:

sudo apt update && apt full-upgrade -y