I've done no work to diagnose where the failure is, but I have Google Fiber, with the supplied Google Wifi device, am on my Google Pixelbook running Google's Chrome OS, and I cannot access Google via IPv6. I don't think I could have a more streamlined setup where Google has full control from end to end to make IPv6 a reality. I can find blog posts by Google talking about the importance of IPv6 adoption, and yet I can't access ipv6.google.com.