Thankyou for running those tests, that is much appreciated.
The answers show that indeed your computer is hijacking your DNS queries and sending them to different DNS servers instead of Pi-hole and all the test servers. Each command is asking a different DNS server to display a text string showing its version. The answers should be different for each one. But instead, they are all the same because it's the same hijacking DNS server responding each time.
Since you are running AVG then this is very likely the culprit. Is this also running on the second computer that you tried, which also exhibited the same symptoms?
AVG has a feature called "Fake Website Shield". This does exactly what you are seeing – it claims to protect you from DNS hijacking... by hijacking your DNS. I know... that's a marketing masterpiece.
You need to turn this feature OFF and have it stay off in order to use Pi-hole. This page claims to show how to turn it off.
Can you please try turning it off on the main computer that you've been using, and then run the nslookup tests again please?
Every time you enter the URL (web address) of a website, such as www.example.com , into the address bar of your browser, the URL is translated to the IP address (Internet Protocol address) of the web server where the web page that you want to access is stored. Fake Website Shield provides an encrypted connection between your web browser and AVG's own DNS server to prevent hijacking and ensure that the displayed website is the authentic one.