https://openwrt.org/docs/guide-user/services/dns/adguard-home#dns_interception - brief rundown is there.
you will require the updated rules as per nft tables if you are using the new builds.
Note this only blocks/redirects regular DNS. you will require extra rules for DOH etc.
:edit: you may also want to read the thread I made about manual / opkg installs of AGH.