Once everything is set up and working.
First find the location of 'startkomga.sh'. You can find out by right-click -> properties -> Location and copy that. Ideally it should look something like
/home/YOURUSERNAME/.../komga
Open terminal and run cd /etc/systemd/system. This should move directories to the location where we will setup the autostart service
Write sudo nano komga.service and press enter. This should open a text editor like terminal window. Write the following
[Unit]
Description=Komga
After=network-online.target
[Service]
ExecStart=/usr/bin/java -jar /home/YOURUSERNAME/.../komga/komga.jar
WorkingDirectory=/home/YOURUSERNAME/.../komga
Type=simple
Restart=always
User=YOURUSERNAME
[Install]
WantedBy=multi-user.target
Description can be changed to whatever it is to your liking but remember the path should be as in your device (that is for these /home/YOURUSERNAME/.../komga/) and also replace the USERNAME with yours.
Press ctrl + S and ctrl + X to save and exit the text editor
Finally type the following command to enable the service
sudo systemctl enable komga.service
Either reboot or run sudo systemctl start komga.service immediately.
If you reboot or whenever you turn on the Linux device it will automatically start.
IMPORTANT NOTE: Not sure of other device, my raspberry pi takes around 2.5 minutes from switching on to getting 'localhost:8080' to work. Maybe it will be faster with other device but hope you all wait for a few minutes before declaring its not working.
Open terminal and run sudo systemctl disable komga.service. Alternatively, you can use sudo systemctl stop komga.service but this will stop while the system is running, that is, reboot will auto start as usual.