A quick 'n dirty script to remove theIptables redirection for ports 80 and 443 of k3s from one IP. Substitute the IP in ADD_LINE with the one you don't want k3s to redirect. Add the script as "ExecStartPost" to /etc/systemd/system/k3s.service.

patch-k3s-iptables.sh

#!/bin/bash

#############################
# Author: Till Wiese/m3adow #
#############################

set -euo pipefail
set -x


LOOP_UNTIL=0
PREPORT_LINE="-p tcp -m tcp --dport"
ADD_LINE="! -d 192.168.1.10"


change_rules () {
  RULEFILE="$(mktemp)"
  iptables-save > ${RULEFILE}

  # Extract the full CNI-DN name
  CNI_DN="$(grep -P ':CNI-DN' ${RULEFILE} | head -1 | grep -oP 'CNI-DN-\w+')"
  for MYPORT in 80 443
  do
    perl -p -i -e "s/(-A ${CNI_DN} ${PREPORT_LINE} ${MYPORT})/\1 ${ADD_LINE}/" ${RULEFILE}
  done

  iptables-restore ${RULEFILE}
  rm ${RULEFILE}
}

while getopts "w" opt
do
  case $opt in
    w)
      LOOP_UNTIL=1
  esac
done

while true
do
  # Extract the full CNI-DN name
  # As it this command may fail, leaving CNI_DN empty, "set +e" is required
  set +e
  CNI_DN="$(grep -P ':CNI-DN' <(iptables-save) | head -1 | grep -oP 'CNI-DN-\w+')"
  set -e
  if [[ $CNI_DN ]]
  then
    change_rules
  else
    if [[ $LOOP_UNTIL == 1 ]]
    then
      sleep 1
      continue
    fi
  fi

  break
done