If you are trying to install extensions on VSCode but you can’t. Try to visit this site from your browser:
Most probably you will get a “This site can’t be reached” message, to solve this you have to change your default DNS to google free public DNS
8.8.8.8
8.8.4.4
If that may not work for you then yo can try to change the DNS for IPv6 to:
2001:4860:4860::8888
2001:4860:4860::8844
Here is a link for more details on changing the DNS to google DNS