With IPv6 you don’t forward ports at all. The device already has a public address.

That's why I said "open ports", not "forward ports".

Stateful firewalls are very much a thing on v6. Many mobile ISPs don't allow incoming connections by default, for example.

Many CPEs (home routers) also come with a v6 firewall (I'd guess it's probably more common than not?), and not everybody has admin access to theirs.

That's the addressing problem, although I have some bad news on that: NAT is used with IPv6 in some places.

The reachability problem is, even with public addresses, sometimes you have to do the same thing to "configure port forwarding" with stateful IPv6 firewalls as with double or triple NAT IPv4.