Earlier quoted context omitted.
It does more than you think it does. GitHub may not support IPv6 and Apple can't force them, too, but the GitHub App on iOS is in most cases using DNS64 to get an IPv6 address to a NAT64 gateway to the GitHub IPv4 addresses, and all that just works today, in part because Apple forced apps to support "I'm always going to give you an IPv6 address, even if you know your own service isn't going to naturally return one".
I was not proficient enough to understand that on my own. ELI5 is that this requirement forces apps to support running on IPv6-only networks where DNS calls return special IPv6 addresses for IPv4 hosts and ISP (usually mobile) does IPv6 to IPv4 NAT. That does sound useful.
[1] IPv6 makes hand-offs between radio towers (cells) a lot easier if the towers don't also have to manage scarce IPv4 addresses/NAT44 configurations and complicated DHCPv4 handshakes to setup/change IP addresses regularly; plus mobile networks in general have a lot of devices today, some have way more than other types of ISPs so IPv4 scarcity was something they could feel directly on their corporate bottom lines.