While true script not running at boot

I have a script that is meant to work with a UPS Hat for a Raspberry Pi 4b. I am running Ubuntu 21.04 server 64 bit. When I run the script manually from /home/user/ups.sh it works great. However, after following the instructions and creating an rc.local file I cannot get the script to start automatically at boot. I have placed the script into the /user/bin/ directory and done a chmod +x on it.

#!/bin/bash

#GPIO17 (input) used to read current power status. 
#0 - normal (or battery power switched on manually). 
#1 - power fault, swithced to battery. 
echo 17 > /sys/class/gpio/export;
echo in > /sys/class/gpio/gpio17/direction;

#GPIO27 (input) used to indicate that UPS is online
echo 27 > /sys/class/gpio/export;
echo in > /sys/class/gpio/gpio27/direction;

#GPIO18 used to inform UPS that Pi is still working. After power-off this pin returns to Hi-Z state. 
echo 18 > /sys/class/gpio/export;
echo out > /sys/class/gpio/gpio18/direction;
echo 0 > /sys/class/gpio/gpio18/value;

power_timer=0;
inval_power="0";

ups_online1="0";
ups_online2="0";
ups_online_timer="0";

while true
do
    #read GPIO27 pin value
    #normally, UPS toggles this pin every 0.5s
    ups_online1=$(cat /sys/class/gpio/gpio27/value);
    
    sleep 0.1;
    
    ups_online2=$(cat /sys/class/gpio/gpio27/value);
    
    ups_online_timer=$((ups_online_timer+1));
    
    #toggled?
    if  (( "$ups_online1" != "$ups_online2" )); then
        ups_online_timer=0;
    fi
    
    #reset all timers if ups is offline longer than 3s (no toggling detected)
    if (("$ups_online_timer" > 30)); 
    then
        echo "$ups_online_timer";
        
        ups_online_timer=30;
        power_timer=0;
        inval_power=0;
        #echo "UPS offline. Exit";
        #exit;
    fi      

    #read GPIO17 pin value
    inval_power=$(cat /sys/class/gpio/gpio17/value);
    
#   echo $inval_power;
    
    if (( "$inval_power" == 1 )); then
        power_timer=$((power_timer+1));
    else 
        power_timer=0;
    fi
    
    #If power was not restored in 60 seconds
    if (( "$power_timer" == 600 )); then 
        #echo $power_timer;
        echo "Powering off..."
        sleep 2;
        systemctl poweroff; #turn off
        exit;
    fi  
done

this is what I have in the rc.local file

#!/bin/sh -e
#
# rc.local
#

bash /usr/bin/ups.sh &

exit 0

I have been searching google for days and I have tried cron and systemd files and nothing seems to work. Hopefully there's a kind soul out there that has an answer. Thank you.