Entire process of installing bringup manually using a systemd service.

1. Remove existing bringup launch files using rosrun

rosrun robot_upstart uninstall robot_uppstart_service

Note : robot_upstart_service replace this with your service name without .service extension.

2. Create a bash script for roslaunch to upstart your robo. (For Simplycity I'll call this launch.sh)

#!/bin/bash

counter=10  # Set counter variable to 10

echo "home = $HOME"
source /opt/ros/noetic/setup.bash

source /home/amrita-acrux/ros1_ws/devel/setup.bash

export ROS_HOSTNAME=$(hostname -I | awk '{print $1}')

# Function to check and source the file
check_and_source() {
    if [[ "$ROS_HOSTNAME" == *"localhost"* || -z "$ROS_HOSTNAME" ]]; then
        source $HOME/.bashrc
        return 0  # Success
    else
        return 1  # Failure
    fi
}

# Attempt to source the file counter times
while [ $counter -gt 0 ]; do
    check_and_source
    if [ $? -eq 0 ]; then
        ((counter--))
    else
        break
    fi
    sleep 1
done

# Check if the loop was successful
if [ $counter -eq 0 ]; then
    echo "DIDN'T WORK"
else
    echo "LET'S GOO"
    roslaunch ROBOT_FIRMWARE ROBOT_LAUNCH_FILE.LAUNCH
fi

Note, here replace ROBOT_FIRMWARE with Your Robot's Package name.
and Replace ROBOT_LAUNCH_FILE.LAUNCH with your robot's Laucnh File.

IMPORTANT. (Make sure the file you created has executable permissions)

chmod +x launch.sh

3. Create a SystemD service for a specific robot user.

on this path /etc/systemd/user/robot_bringup.service

[Unit]
Description=RigBetel Labs ROBOT UPSTART SCRIPT
After=NetworkManager.service

[Service]
Type=simple
ExecStart=/path/to/your/above/bash/script.sh
Restart=always

[Install]
WantedBy=default.target

Note If Possible try changing $HOME with your full path as it will be more accurate.
Replace /path/to/your/above/bash/launch.sh with the path to your launch.sh shell script.

4. Now Enable the systemd service for that specific user only

systemctl enable --user robot_bringup.service

NOTE : We are not running the below command with SUDO, don't use sudo as we are doing it for the robot user only.

5. Check whether the systemd service is started correctly or not. Some helpful commands are given below.

systemctl start --user robot_bringup.service

Check Status

systemctl status --user robot_bringup.service

To check Logs

journalctl --user-unit robot_bringup.service

6. Enable a Lingering session

Note this is the most important step.
Why are are doing this? We need something to start a user session so that after each boot it should start the systemd service automatically.

loginctl enable-linger

Note, make sure you are doing it from the same user you configured the service
OR

loginctl enable-linger robot-username