@jan Thanks for checking and helping me and I really appreciate for your time in helping others and ofcourse for this awesome project 
Yes, I have provisioned Ubuntu 20 on oracle cloud and on a fresh installation I have followed exact same steps as give in this article https://docs.n8n.io/reference/server-setup.html#example-setup-with-docker-compose (for env i have used /etc/environment)
After docker compose up, I am able to access via external subdomain https://n8n.example.com but on visiting the external IP on that domain (152.124.125.126), it is allowing me with TRAEFIK DEFAULT CERT.
Below are the screenshots.
IP Access
Its binding and stopping the connection too as I am getting 404 on further accepting the default cert but I was thinking can I just re-route this IP to domain instead of 404 page not found?