wikipedia[.]org/wiki/IPv4
wikipedia[.]org/wiki/IPv6
docs.microsoft[.]com/en-us/troubleshoot/windows-server/networking/configure-ipv6-in-windows
I was given a 5-6 year old PC, & after resetting the Win10 it came with [to get the drivers], updated it to the latest v. 20H2. Then came a surprise... searching with Google brought up a page that the PC was using IPv6 to IPv4 tunneling, which would soon be Not supported, and had to go through a Captcha to get search results (?)!
IPv4 is what the Internet originally, and to a great degree still uses -- every web page gets a numerical-based address, rather than go by whatever name, e.g. SomeName[.]com. But there aren't enough numbers in the scheme for all the web sites out there, so they came up with the more complicated IPv6. Everybody was supposed to switch over years ago, but it still hasn't happened. One of the methods to make things work before the switch to IPv6 was complete, was/is to use IPv6 to IPv4 tunneling, which you might not have [probably haven't] heard of.
In this case that tunneling was something Win10 had apparently done, set up on it's own. Problem was there's not a load of info out there on how to make it stop -- I finally found one web page at Microsoft[.]com that tells you how to turn off this tunneling by adding a registry key, and wanted to post that link. Far as I can tell this was either something that Dell had originally set up on this PC, that was carried over after the Win10 update, or it's something that was added when I updated the latest version of Win10, using an ISO I got with the Media Creation Tool. In case it was the latter, I figured posting that link might be pretty helpful. ¯\_(ツ)_/¯
Note: the web site says: "The IPv6 functionality can be configured by modifying the following registry key:" It doesn't mention that you'll probably have to create that registry key. To do so, open Regedit [right click Start Button, then click Run, type in Regedit, & click OK], go to the address given [HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ Tcpip6\ Parameters\, right click on the space on the right, selecting new DWord, name this new key DisabledComponents, and to turn off IPv6 to IPv4 tunneling, set the *decimal* value to 1.