Github is one of the most idiotic IPv4 exclusive services. Microsoft and Azure has all the knowledge and equipment to make IPv6 available to practically any site, but Github seems afraid to ask. They had IPv6 for a short while and turned it off later.
ZScaler is worse on a practical level. I have to disable IPv6 system-wide else I can't access internal services (it only routes IPv4). The crazy thing is that they call out VPNs for being archaic, but force users to use an even more archaic technology.
Bless you for mentioning that ZScaler doesn’t play nice with IPv6 - this gives me another possible cause for why a certain MSFT distributed app sometimes, but not always, installs on our users’ PCs when ZScaler is enabled, but works with it off.
https://github.com/orgs/community/discussions/10539 is full of people voicing their grievances but I don't think Github is paying this issue any attention anymore.
Luckily almost all providers or IPv6-only networks also offer NAT64 or similar NAT mechanisms to make IPv4 addresses reachable.