On my Ubuntu-based distro (Linux Lite), how to auto delete all network connections, disable Wi-Fi and networking as part of booting process?

My end goal here is to have no saved network connections, no enabled Wi-Fi or networking each time I boot up my computer, so that I have to go through a sequence of steps in order to access internet. The purpose is to moderate my sceen behavior. My current way is through creating a script that uses 'nmcli' and run at startup using crontab's @reboot. But It's not working. Here is the script

#!/bin/bash

# this script disables wifi and networking

echo 'Deleting all existing connections...'
# nmcli is a command-line interface for networkmanager
# 'nmcli connection delete' -> simply deletes a connection by ID, UUID or others
# we use 'nmcli connection show' along with some filter to extract UUIDs for all conections
# TODO enable deletion of a particular connection
#connections_list=$(nmcli connection show | grep -oP '\s(\S+-\S+-\S+-\S+-\S+)\s')
#for connection in "$connections_list"; do 
    #nmcli connection show "$connection"
    #if (($? != 0)); then 
        #echo "something went wrong while deleting connection $connection" >&2
        #exit 1
    #fi
#done
nmcli connection delete $(nmcli connection show | grep -oP '\s(\S+-\S+-\S+-\S+-\S+)\s') 
if [[ $? -ne 0 ]]; then
    echo 'shit happens while deleting connections' >&1 
    exit 1
fi
echo 'All connections were deleted! now, you will have to type SSID and password again'

echo 

echo 'Disabling Wi-Fi...'
if ! nmcli radio wifi off; then 
    echo 'nmcli, command disabling wifi, is not satisfied for some reason' >&2
    exit 1
fi 
echo 'Wi-Fi is disabled.'

echo 

echo 'Disabling networking...'
if ! nmcli networking off; then 
    echo 'nmcli, command disabling networking, is not happy' >&2 
    exit 1
fi
echo 'Networking is disabled.'

echo

echo 'All is good'
echo '==============================='
exit 0

Here is the corntab line (created using sudo crontab -e) @reboot /home/noor/bin/go-offline-1.0 >> /home/noor/go-offline.log 2>&1 Contents of log file:

Deleting all existing connections...
Error: NetworkManager is not running.
Error: NetworkManager is not running.
shit happens while deleting connections

I guess that at the point of executing my script in the boot process, NetwrokManager is not yet activated. Also after a quick exchange with ChatGPT, I tried to make script run as part of the shut down process rather than at startup using systemlc or sth, but it didn't work for some reason. I don't see reason to mention its details. I had an idea to alias poweroff command so that it executes my script then shut down the computer. I don't know whether it's a good idea but I am looking for a better solution anyway. I welcome all useful responses related to any part of this, including fixes to this method or completely different approach. Thank you!