I am new to the Flint router and OpenWrt, so please be patient. I have set up Cloudfare as DNS in Internet. I have also set up AdGuard Home and DNS over https (DoH).
Could you please provide screenshots of your current settings under Admin Panel → Network → DNS and Applications → AdGuard Home?
Based on the current DNS leak test results, it appears that AdGuard Home is enabled, but the default upstream DNS servers (Google DNS and Quad9) have not been changed, which would explain the results you are seeing.
If you would like to use Cloudflare instead, you can go to Admin Panel → Applications → AdGuard Home, click Settings Page to open the AdGuard Home configuration interface, and then go to Settings → DNS to configure the upstream DNS servers as Cloudflare DNS.