New UI is still available, but the naming convention is now changed to notify the purpose of using it or what most customers use it for.
Was the new UI working in the older versions? Because apart from just enabling trailblazer on port 4431, you need to also ensure the interface hostname (to which you are trying to connect to) is resolvable to the IP address via the DNS server configured.
You can run "tcpservices" command to verify if the ESA is listening on port 4431, run simple telnet or curl tests. If this works, then ensure the DNS resolution is sorted for its functionality.