In your IIS, just configure binding to make sure the incoming request from the Internet is recognized by IIS. You also need to make sure you have no rule in Network Security Group (NSG) blocking port 80. Or if there is a NSG, you need to create an inbound rule to allow port 80.
Why does windows (file) explorer try to connect to port 80 but it can connect to the internet And now for what I think is the interesting part: running wireshark with ip.addr == local.ip.add.ress and ip.addr == server.ip.add.ress tells me that it tries to connect over http. Why closing port 80 is bad for security Dec 09, 2016 Port forwarding - Wikipedia
How To Access A Local Website (localhost) from Internet
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Port 80 is the non-secure incoming/listening port of a webserver. It can be 80 or 8080 (both are not same, but usually not secure). Port 443 is the secure counterpart of 80. Like 8080, secure port is also denoted as 8443 (443 and 8443 are not same
Understanding Port Forwarding- Beginners Guide Apr 11, 2020 Preventing SMB traffic from lateral connections and