if I share my files with this: fopnu:channel:d5quieifhxxxxxxxxxxxxxxxxx/xxx, then other people can see my real ip address like "xx@127.x.x.x", and then know where I live. I really don't like it.  

How can I hide my ip address?

You can use a VPN to do this, but a VPN is only effective if you trust them more than your ISP. I use ProtonVPN and I deem ProtonVPN, Mullvad, IVPN, RiseUP VPN, Incognet VPN, Psiphon, Lantern and Cloudflare Warp to be trustworthy.

Is there a way to hide this ip address  "@127.x.x.x" easily?

Hide from whom? From yourself? Put some opaque tape on your monitor.

FOPNU is a completely traditional peer-to-peer application. Peers connect to other peers directly, there is no traffic relaying, and no promises of anonymity. Even if addresses are not shown in the interface, you can trivially observe the network connections to figure them out. Try running netstat.

If you download or upload something that makes you want to hide your IP address, you can be sure that the other side has already put it on paper.

127.x.x.x is your LAN local network addressing. While something like 84.12.128.12 would be your visible, public Wide Area address. I would suggest the FOPNU programmer add full LAN support if it doesn't already for connecting to a local area networked telecommunications community or region via MESH LAN or Wireless networking.

If SHTF (regional, global wars break out) happens, as long as local peers have power, they can share files, message one another et al if FOPNU fully supported LAN wireless networking. 127.0.0.1, 127.0.1.x et al. While WAN Global WWW cables and continent relays are cut or deliberately shut down as repeatedly threatened by Western leaders on their own WWW shared internet sharing, those LAN-Mesh networks would, could still function.

New to Mesh Networking or the LAN concept, here are some helpful links focused on the BATMAN p2p protocol via MESH

A brief introduction to wireless Mesh BATMAN Networking https://www.open-mesh.org/projects/batman-adv/wiki/BATMAN_IV
https://en.wikipedia.org/wiki/B.A.T.M.A.N.
https://github.com/benkay86/openwrt-batman-tutorial
https://downloads.open-mesh.org/batman/papers/batman-status.pdf
https://wiki.p2pfoundation.net/BATMAN