There is no such thing as the basic Nucleus Web GUI with a Windows based server install, as others have commented already.
You will have to find other ways of how to get such functionality, and I’m guessing, that with one of your Room remote devices you’ll be able to Remote-Desktop into that machine to do your housekeeping.
However, did you also use the Control 4 Roon interface to interact with what’s played where?
If so, that’s been made available to other OS‘s than Roon Nucleus and you‘ll find details regarding getting it to work here.
That said, and if you’re ready for some DIY, replace whatever’s broken in your Nucleus, install ROCK yourself, and support will be able to remotely restore genuine Nucleus functionalities for you.