Run macchanger on boot init script. The original auto spawn doesn't work since it's nearly 10 years old. Should work on all debian based systems, since it's a SysV style init script. Tested on devuan+openrc . Can be easily strict-chained with NM. Requires iw package to obtain interface.

mac-randomizer

#! /bin/sh
#
# Randomize computer's MAC address on boot before the network-manager service.
# Using with Kebablord/macchanger-ng is adviced since
# original repo didn't receive any PR for nearly 10 years.
# Script also exits safely on any fail so you can safely chain it with
# network-manager updating Required-Start parameter from NM's init script.
# This gist is created for educational purposes only.
# 
# No Copyright (c) 2023 Kebablord Corporation.
#
### BEGIN INIT INFO
# Provides:          mac-randomizer
# Required-Start:    $remote_fs dbus udev
# X-Start-Before:    network-manager
# X-Stop-After:      network-manager
# Default-Start:     2 3
# Default-Stop:      0 1 6
# Short-Description: mac address randomizer
# Description:       Randomize MAC address using macchanger.
### END INIT INFO

PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
SCRIPTNAME=/etc/init.d/mac-randomizer

. /lib/lsb/init-functions

type macchanger 2>/dev/null 1>/dev/null || (log_failure_msg "macchanger not found."; exit 1)

#iface=$(ifconfig | grep -P '^w.*?:' | awk -F ':' {'print $1'})
iface=$(iw dev | grep Interf |awk -F 'Interface ' '{print $2}' | head -n 1)
[ -z $iface ] && (log_failure_msg "network interface not found."; exit 1)

# Exit safely in any fail. It's important because you may
# want to use this script in strict chain with network-manager
safe_exec() {
  $* || exit 1
}

check_if_changed() {
  status=$(macchanger -s $iface | awk '{print $3}' | uniq | wc -l)
  [ 2 -eq $status ] || false && true
}

# This pause functions are used to revert services
# back to their previous state after stopping them.

pause_nm() {
  if (pidof NetworkManager>/dev/null);then
      safe_exec service network-manager stop
      safe_exec $*
      safe_exec service network-manager start
      return 0
  fi
  safe_exec $*
}

pause_iface() {
  if (safe_exec ip link show dev $iface | grep UP);then
     safe_exec ip link set dev $iface down
     safe_exec $*
     safe_exec ip link set dev $iface up
     return 0
  fi
  safe_exec $*
}

case "$1" in
  start)
        pause_iface macchanger -r $iface >/dev/null 2>/dev/null
	if check_if_changed;then
            log_success_msg "Randomized MAC address."
	else
	    log_failure_msg "Couldn't randomize MAC address."
	fi
        ;;
  reset)
        pause_nm pause_iface macchanger -p $iface
	;;
  stop)
	true
	;;
  reload)
	pause_nm $0 start
	;;
  status)
        if check_if_changed; then
            echo "MAC spoofing enabled:"
	    macchanger -s $iface | xargs -I % printf "     %\n"
        else
            echo "Address is default hardware MAC, not changed." >&2
        fi
	;;
  *)
	echo "Usage: $SCRIPTNAME {start|reload|reset|status}" >&2
	exit 1
	;;
esac

exit 0