Cloudflare tunnel private network

Can I use Cloudflare Tunnel to join two local networks together?

My brother lives in another country and I wanted to share some local server resources with him. I did it until now by getting a domain and exposing the server to internet. I want to try out a different approach that does not expose the server and does not use a domain name.

So few possible connection flow scenarios we can have is:

  1. PC → Router → Internet → Router → Server
  2. PC → Router → Internet → Server
  3. PC → Internet → Router → Server
  4. PC → Internet → Server

Routers mentioned in these scenarios are your usual home routers. My Brother sometimes uses the mobile data to connect to internet which does not go through the typical home router.

The reason Why I am emphasizing the Home routers presence here is that, when I looked through the docs and tried to follow the bare minimal guide they had, it seemed like Cloudflare tunnel hooked up to an existing local network ip that is given by some home router.

When I tried to follow the guide with a server sitting right behind the modem and getting only public ip I could not successfully configure the tunnel.