I just tried turning off wifi on my phone. After googling what is my ip and pinging the IPv6 address from another IPv6 device, it doesn't work. Whether it's a firewall/NAT/whatever is irrelevant. IPv6 as deployed does not provide p2p.
PS - typing the IPv6 address was super annoying and error prone compared to IPv4.
Your mobile network is probably still V6 at the core. They're either giving you V4 at the endpoint or your phone is hiding V6 from you. Android or iOS? Apple stuff is V6 native now. Android's gonna be mixed.
Depends on the carrier network though. I am on Spectrum (Verizon network) in Ohio and get V6 with CGN for V4. My wired ISP provides dual stack.
Never tried but I somehow doubt it. Standard issue UDP hole punching absolutely does work though.
You still usually need hole punching with IPv6 if there's any kind of firewall in the way, but unlike IPv4 with NAT it's virtually 100% successful. Even if IPv6 NAT is deployed there's usually a 1:1 internal/external IP mapping making hole punching 100% successful.
Phone data traffic is proxied or NATted for qos and other purposes, even with IPv6.
It works better outbound than the old model though. I use iSH to get a Linux shell and with a mini Bluetooth keyboard I work on some hobby projects on the train from my iPhone.
PS - typing the IPv6 address was super annoying and error prone compared to IPv4.