Simple fix for a debian linux upgrade to bullseye. Some packages will show an error message like `/usr/bin/perl: /lib64/libcrypt.so.1: version `XCRYPT_2.0' not found (required by /usr/bin/perl` and you have to link the new spot of the library. Update: I have to run it before installs and upgrades and everything is fine.

repair-debian-lib-XCRYPT_2.0.sh

#!/bin/bash
# Needed for debian upgrade
# atm from buster to bullseye the linked libs are broken 
# see: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=951880

LIB="libcrypt.so.1"


# Checks if the executer has super user permissions.
#
# @exit 2 if the user has no super user permissions
function validateRootPermissions() {
    if [[ $(/usr/bin/id -u) -ne 0 ]]; then
      echo "[ERR!] script must be run as root (sudo) and you're not root."
      exit 2
    fi
}

# Validates the existing of:
# - the source library exists (normally a link to the lib file)
# - both destinations are symlinks
function validateLibsExists() {
    if [[ ! -f "/lib/x86_64-linux-gnu/${LIB}" ]]; then
        echo "ERROR: Library file </lib/x86_64-linux-gnu/${LIB}> does not exists."
        exit 1
    fi

    if [[ ! -L "/lib64/${LIB}" ]]; then
        echo "ERROR: Library symlink </lib64/${LIB}> does not exists."
        exit 2
    fi

    if [[ ! -L "/lib/x86_64-linux-gnu/${LIB}" ]]; then
        echo "ERROR: Library symlink </lib/x86_64-linux-gnu/${LIB}> does not exists."
        exit 3
    fi
}

# Analyse the src and dest libs and if they link this src lib.
function analyseLibLinks() {
    validateLibsExists
    local correctPathSrcLib="$(readlink -f "/lib/x86_64-linux-gnu/${LIB}")"

    if [[ $(readlink -f "/lib64/${LIB}") = "${correctPathSrcLib}" ]]; then
        echo "[ ok ] $(ls -la "/lib64/${LIB}")"
    else
        echo "[ERR!] $(ls -la "/lib64/${LIB}")"
    fi

    if [[ $(readlink -f "/lib/x86_64-linux-gnu/${LIB}") = "${correctPathSrcLib}" ]]; then
        echo "[ ok ] $(ls -la "/lib/x86_64-linux-gnu/${LIB}")"
    else
        echo "[ERR!] $(ls -la "/lib/x86_64-linux-gnu/${LIB}")"
    fi
}

# Simple list of the symlinks to check.
function showLibLinks() {
    ls -la "/lib64/${LIB}"
    ls -la "/lib/x86_64-linux-gnu/${LIB}"
}

# Removes the old links and set the new symlinks.
function changeLibLinks() {
    sudo rm "/lib64/${LIB}"
    sudo rm "/lib/x86_64-linux-gnu/${LIB}"
    sudo ln -s "/usr/lib/x86_64-linux-gnu/${LIB}" "/lib64/${LIB}"
    sudo ln -s "/usr/lib/x86_64-linux-gnu/${LIB}" "/lib/x86_64-linux-gnu/${LIB}"
}

# Prints the help to stdout.
function printHelp() {
    cat <<EOF
    Project: rlxcrypt
    Desc:    Repair lib error XCRYPT2.x, XCRYPT4.4 not found.
    Version: 0.0.2
    Infos:   Martin Kock <[email protected]>

    Possible options:
        -a | --analyse          Show the actual linked libraries
        -r | --repair           Change the library links to </usr/lib/x86_64-linux-gnu/${LIB}
        -h | --help             prints this help
EOF

}

# Catch arguments and go
if [[ $# -eq 0 ]]; then
    # starts the main function
    printHelp
else
    case "${1}" in
        -a | --analyse)
            analyseLibLinks
            ;;

        -r | --repair)
            validateRootPermissions
            changeLibLinks
            ;;

        -h | --help | *)
            printHelp
            ;;

  esac
fi

exit 0

After spending even more time on this issue, I found a simple way of fixing all the lib related issues that pop up during the upgrade, since there is a bunch.
Simply install usrmerge, modify the script to remove the files located in the /usr directories when it errors, run till it's finally happy and run the upgrade afterwards. Just works.