How to properly use routing in Next.js with subdomains, with proxying?

Question

React

I have an application on next.js.

The page structure is like this:

pages/
  |-- index.js
  |-- about.js
  |-- admin/
     |-- index.js
     |-- stats.js

2 subdomains are used: example.com and admin.example.com

We use apache as a server with request proxying
Launched a JS application (next start) that runs on port 3000

Added settings to the Apache config:
1) If we are knocking from the main domain, then requests go to localhost:3000/*
2) If we knock from a subdomain (admin.example.com), then requests go to localhost:3000/admin/*

The essence of the problem is as follows.
When I walk through the pages of the main domain (example.com -> example.com/about), the site works like a SPA, the page is not updated, but simply drawn from JS files.
And when I walk on a subdomain, then with each click (admin.example.com -> admin.example.com/stats) the page refreshes.

From errors in JS, I realized that the matter is in routing and request proxying.
I go to admin.example.com -> admin.example.com/stats on the client. JS looks for /pages/stats.js file - it doesn't exist. The page refreshes and thanks to proxying, the /pages/admin/stats.js file is searched for on the first load and everything is displayed correctly.

How can you do a normal job in this case? Maybe somehow specify in the _app.js file - if you are on a subdomain, then look for pages in the /pages/admin/* folder? Or maybe I have not the right approach to this problem at all?