nslookup error: connection timed out; no servers could be reached

Question

My Ubuntu is 20.04.6. Recently, I installed VPN, then I found I cannot connect to the Internet (even after I uninstalling it). I have tried all the methods, but with no luck. Following are commands:

1. nslookup

   connection timed out; no servers could be reached

2. ping website return

   Temporary failure in name resolution

   (ping ip address ok)

3. cat /etc/resolv.conf

   nameserver 127.0.0.53

4. ll /etc/network (no interface file)

   

5. ifconfig

   

6. ip link show

   

7. ip route

   

8. route

Any comment is really appreciated!