Not positive, but I think you left in a reference to real info (twilightparadox.com) instead of “example-fying” it (mydomain.com), in the paragraph just before section 4:

For example say I have home-assistant running on a Pi with the local address 192.168.0.11, I could create a subdomain named ha that has the value mysub.twilightparadox.com then create the following nginx config

server{
	listen 80;
	server_name ha.mydomain.com;
	resolver 192.168.0.1;
	location / {
		proxy_pass http://192.168.0.11/;
	}
}

When nginx sees a request for ha.mydomain.com it passes it to the address 192.168.0.11 port 80.