My ISP offers a plan without IPv4 at a lower price. v4 websites only are served through their NAT64/DNS64 infrastructure and it works really well except for some dumb applications that hardcode the IPv4 instead of using domain names (yeah, and also the ones that rewrite the entire stack in C and only support AF_INET...)
If possible, can you share the ISPs name?
Pretty sure all xbox services use v6 where possible as well.
I am dual stack at home. While my xbox will happily display its ipv6 address my traffic logs still show it heavily preferring ipv4 when actually doing anything.
This is also the reality for many DSL connections these days.