If I enter in browser’s adress bar http://example.com or https://example.com I will see nothing?
Because http prefix says browser to connect to 80 port and https - to 443 port?
Am I right?
Port 80 is the port for non-SSL connections. So for that one you would never need a SSL cert. Only if you run on 443 to use https.
n8n will also run totally fine on port 80. You just have to be aware that the connection is not secure and some services will decline to create webhooks to your n8n instance for exactly that reason.
The problem that you are going to run into running n8n on ports 80 or 443 is that only applications with root credentials can use ports below 1024 since these are privileged ports.
While this is easily doable, it does open up a security risk as any n8n workflow is now running as root. If someone were to get access to your n8n admin interface, they can essentially take over your entire server with ease.