Separated subnets with two routers

Ok, I've done it all again from scratch and now everything works as expected: all the devices on the guest WiFi access the internet but not the "trusted LAN" and the Fritzbox can't seem that at all. :+1:

Now all I need is to be able to let the NAS see the security cameras which, atm it can't. I guess there could be two approaches to this: one is using the VLAN like we tried before, but I'm afraid it's a little bit of trial and error process; the other could be, correct me if I'm wrong, just forwarding the ports (or traffic) from the cameras to the NAS in the Netgear firewall, excluding the need to have a physical cable connecting the NAS second NIC to the Netgear OpenWRT.
I had the idea from what I did to connect it to the other cameras I have in my garage (which is too far to join any home WiFi) via a Wireguard tunnel on another OpenWRT cellular modem/router.

I've tried this latter approach myself but I'm stuck because the NAS can't autodiscover the cameras (which is expected and happening also with the garage cameras) and I don't have an IP address to give to it like I do with those through the Wireguard client where I just fill in the client peer address (10.18.7.x). I've tried set it to 192.168.0.2, but they are not recognized.

A third solution that should work ootb without any modification to the configuration, but involves a little money investment, coul be buying a NAS-compatible USB WiFi dongle (something like this, that on local Amazon is even cheaper than that) so the NAS joins the wireless guest and connects to the camera there. Yes, it'd be weird to have two devices that sit on beside the other connected wirelessly, but whatever!