Shared internal network

Installing and Using OpenWrt
1

Good day. On my router, I configure two interfaces and two Bridge devices br-lan and br-lan2. I did everything according to these instructions. Because of this, two separate networks were formed inside the router

The first br-lan network combines all wired devices connected to the router, and wireless devices connected to the first Wi-Fi network

The second connects only wireless devices connected to the second Wi-Fi network. The difference is that devices on this network access the Internet via WireGuard

One TV with smart TV and the second with Chromecast are connected to the second Wi-Fi network. You need this to watch blocked YouTube. The computer is connected via a wire and is on a separate network, which is why I cannot broadcast the contents of the screen to TV from the computer via Miracast or Chromecast.

In this regard, the question is whether it is possible to somehow combine br-lan and br-lan2 into one internal network, but retain the feature of the second Wi-Fi network connecting to the Internet WireGuard.

2

Nope. If you have two independent L3 networks, bridging them together would defeat the purpose (and likely cause serious problems, too).

You can search the forums for chromecast between networks, mdns repeater/reflectors, and even sonos between vlans for some ideas of how to resolve the issue you're having with casting. Or make sure that the cast source and target are on the same network when you intend to cast.