Why is the DNS server incorrect in Tunnelblick?
Tunnelblick will automatically configure your macOS to use our private DNS servers when a VPN connection is established. If you are using DHCP, please ensure that you check the Set nameserver checkbox.
However, if you have manually configured DNS servers, then regardless of the state of Set nameserver, your manually configured DNS servers will always be the only ones used. We strongly recommend that you configure your device to use DHCP and use the Set nameserver option to ensure that your privacy is not compromised due to DNS leaks.