Thanks a lot for your answer.

I configured it properly, I did the initial config. But the problem is that during this initial config, I can only choose 1 interface on which AGH will listen for the DNS.

I couldn't find those setting anywhere in Adguard unless in the initial configuration that I can no longer access. What was listed was the interfaces and networks I have here in my config file, which means I had to choose between br-lan and br-guest. I chose br-lan. But I couldn't find a way to make it work for both br-lan, br-guest and the internal openwrt internet access for its features. So technically I think AGH works as expected, but I have a problem for adapting my network to be fully compatible.

My adguardhome config file only contains this :

config adguardhome config
        # Where to store persistent data by AdGuard Home
        option workdir /var/adguardhome

And this folder only contains :

root@OpenWrt:/tmp/adguardhome/data# ls
filters      sessions.db  stats.db

So I'm not sure how to access the settings from outside of AGH

I don't have a guest network, but I did install Adguard and now can't download opkg just like you. Let me know if you get a fix.