Hello,
IIS is not required in Symantec Endpoint Protection v. 12.1, as it is replaced with Apache.
Symantec Endpoint Protection Manager 12.1 uses the Apache web server instead of IIS.
If you used a custom IIS web site in IIS, it will be completely replaced with an Apache site after the migration, and additional web server ports must be configured manually.
If you used the default web site in IIS, the migration will modify the default IIS web site with a proxy that redirects IIS requests to the Apache web server; additional ports will still work correctly in this case.
Check this:
Symantec Endpoint Protection Manager 12.1: Migration from 11.x Manager on custom IIS web site uses only the first IIS Port
How to bypass the IIS proxy after upgrading to Symantec Endpoint Protection Manager 12.1