There are two ways to install AGH:
- opkg (this is how you did it) - described here: https://openwrt.org/docs/guide-user/services/dns/adguard-home
- manual - described here: [How-To-Updated 2021] Installing AdGuardHome on OpenWrt [Manual and opkg method]
Quoting from the manual installation thread:
I suspect there is typo in the documentation: https://openwrt.org/docs/guide-user/services/dns/adguard-home#data_files, there should be nothing in /opt
when installing via opkg.