Context:
People have been asking for IPv6 Support on GitHub since years (probably a decade by now)
... and someone even got so annoyed that they decided to setup a dedicated website for checking this: https://isgithubipv6.live/
Not at all only. At times you have both IPv6 and IPv4 and other times you can still get IPv4 at no additional cost like when you run your own router or modem. The layperson will be given IPv6 by default, but it's not the only thing you can get.