You can also use Tor as IPv6 proxy in a pure IPv4 network (or as IPv4 proxy in a pure IPv6 network), recent versions of Tor can work under pure IPv6, gaining privacy and connectivity simultaneously. The speed is not actually too bad for web browsing, although not ideal for SSH. But still comes handy sometimes, I'm used it before to clone packages from GitHub on IPv6-only servers.
How does github not have an AAAA record in 2020?? The faster people move to gitlab the better. ipv6 servers are not at all rare. Useful for individual use since you can save $1/month by dropping a useless for personal use feature.
Last time I launched a new website it took less than a month for someone to let us know that we'd forgotten to configure a AAAA and our site was inaccessible for them. And that was at new website traffic volume.
So yea, GitHub definitely knows about AAAA records and has intentionally decided not to have one. The question is: why? They must have a reason. Maybe even a good one. I'm curious.
A broken AAAA record, perhaps. Sometimes the AAAA is invalid or broken without getting noticed by the sysadmin. I've personally reported broken AAAA records before.