Big cloud providers have good IPv6 support. The long tail is terrible. We work with ~200 different hosting providers, half of them have no IPv6 support at all,

Big cloud providers have good IPv6 support. The long tail is terrible. We work with ~200 different hosting providers, half of them have no IPv6 support at all, another ~15% it only works occasionally and they clearly don't monitor it. There's also a fair number of still popular libraries and frameworks that don't handle IPv6 well. Maybe not in their latest release, but in their more popular older ones.