With Gargoyle version 1.13.X |OpenWrt 19.07 then dns https proxy does work out of the box.
1. Add Plugin Sources
- Both base and package from openwrt release 19.07.9
2. Remove dnsmasq and install dnsmasq-full
3. Install https-dns-proxy
4. Test the setup using https://openwrt.org/docs/guide-user/ser ... -dns-proxy
No need changing wan dns or adding firewall user rule.