How to route the traffic from a wireless to wireguard

Installing and Using OpenWrt Network and Wireless Configuration
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You need to do Policy Based Routing and you have 3 options:

  1. mwan3 package
  2. pbr package
  3. a set of rules/routes for each internet connection.

If every wifi interface is bridged in the lan network, then you can manually select the IPs which are used in the 5G wifi and route them via the wireguard tunnel. If this is not possible to achieve, then you need to create a separate network for the 5G wifi and route every packet coming in from the 5G network to the wireguard tunnel.