How to restrict users of other roles from seeing the site administrator details?
That's kind of a "asking for a module to do X" question, which is not really allowed but I do think it is a very common task.

There are a few approaches/modules to this, we are using the combination of https://www.drupal.org/project/userprotect to prevent users from editing users that already have the administrator role, and https://www.drupal.org/project/roleassign to prevent them from giving the administrator role to a user that they are allowed to edit.

There is also https://www.drupal.org/project/administerusersbyrole, which in the 8.x-2.x branch attempts to solve this without requiring users to get the administer users permission, which is more safe, but it also requires core patches because a lot of things in core itself can't really deal with users being able to edit other users without that permission yet.