Please set the dns in ipv4 setting ( in windows) to next dns and also set the dns in your router to nextdns, flush dns cache in windows and do a retest to see whether you get your desired results. If you get what you are looking for after using the above mentioned settings it would mean that the adguard in your system has some issues in using an external DOH server. you can then try uninstalling adguard completely and reinstall it to see whether the issue is solved or not.I copy the more elegant explanation from @JoyousBudweiser
3. You can also use New desktop adguard (Version7.5) and use nextdns as a doh/Dot resolver. (Go to Settings> Dns> Add a custom dns "https://dns.nextdns.io/xxxxxx" Replace "xxxxxx" with your configuration id which you can find in your nextdns account).
For chosing the AdguardDNS I just had to select the AdguardDNS server (inside the Adguard Desktop APP) instead of the freshly created NextDNS Server. Thats the way I did my testing.
To be honest I forgot to flush the DNS cache as kindly pointed out. But even after doing it I get the same results.