Is any server response closed from indexing?

Question

Web development

If I want to create an empty subdomain and proxy its directories to different projects like /munin, /cockpit, /nagios (by the way, is this a good idea?), is it possible to somehow close the subdomain from robots without proxying it to the folder with robots. txt?
I just don’t want it to be in the lists on sites in the results of "all subdomains of the site"

Answer 1

You will have authorization there, right? That is, the robots will not go beyond the authorization page.
If there are no external links to this subdomain, then they will never find it.

without proxying it to a folder with robots.txt

why proxy? Let this subdomain have its own robots.txt with content

User-agent: *
Disallow: /