I had a very similar issue. My configuration included a guest network, so I'm not sure whether that applies exactly to your situation. However, I couldn't find a way to resolve it. I ended up having to factory reset it, after which point things began working properly. No idea which setting broke me, but setting up guest WiFi blocked all IPv4 traffic from all of my devices, even though they weren't on the guest network.

Check what mode you're open WRT devices in. Are you getting DHCP information from your internal clients?

Have you tried pinging a known external IP (e.g. 8.8.8.8) to see if it's visible from the LAN devices? It could be something as simple as DNS not being setup correctly. Also, have you verified that the LAN devices are being assigned an address?

I bet you its our firewall setup. You need to go to the firewall tab and make sure that traffic is getting forwarded to the outside.

Also verify your devices are getting assigned IPs