1. vi /etc/systemd/system/gotify.service

   [Unit]
   Description=gotify
   After=network-online.target
   Requires=network-online.target
   
   [Service]
   User=UsernameOfGotifyUser
   WorkingDirectory=/path/to/folder/containing/gotify/binary/
   ExecStart=/path/to/gotify/binary/gotify-linux-amd64
   Restart=always
   
   [Install]
   WantedBy=multi-user.target
   

2. systemctl daemon-reload
3. systemctl start gotify

Simple as that!

Check Gotify is running with the systemctl status gotify command, and if all is well, start Gotify at boot with systemctl enable gotify