Mesh Configurations and Setup for Guest AP

Hi everyone, I currently have my main router (BananaPi-R4) and a extender i had (Netgear EAX12 v2) configured as a mesh network, both with OpenWrt. On my main router i have some services running like NextDNS, Wireguard (client and server), QoS, etc. The main router have just 1 AP in both freqs (2.4Ghz and 5Ghz) which is my main network (Lan) but i want to add another AP for my Guests, where they cant access my Lan devices, and don't use NextDNS or WG. How should i proceed to configure it? I followed this and i already have a Guest Network working, at least on the main router. Should i follow the same procedure on the EAX12? Like creating the br-guest device, then the interface, wireless AP and firewall rules?

Let's be sure to clarify...

How is your additional AP connected to your main router? Ethernet or wifi?

Sorry, forgot to mention it. Its connected via Wifi. I followed this guide.