why make it complicated?
Just add AdGuardHome to your router, configure it to point at whatever upstreams you want (it does all the encrypted DNS, DoH, DoT, DoQ), add in your filters for adblocking and go on to doing something more important... like opening a new beer.
Use cloudflare or google or even any of the number of privacy focused DNS providers that are free.
Thats the most recent writeup to use AGH. All you have to do is move openwrt's dnsmasq to a different port and then use the installer script. i HIGHLY suggest you use the new 107 edge build and keep an eye on your diskspace. Do NOT use the OpenWRT opkg package. It is version 104 and every time you reboot your router you will have to resetup AGH as it stores its config on the /tmp.
(edit) AGH team are working on improving their DHCP setup so long term you'd just disable DHCP on OpenWRT and handle it all from AGH. Right now thats not advisable unless you have a simple setup as their DHCP is kinda limited and no match for the OpenWRT setup.)