IPv6 address of jail not visible from outside and no hardware id available

[CaptainCaptain]

Hello,

I have the Nextcloud plugin installed and set IPv4 and IPv6 to autoconfigure. IPv4 works fine, but I still have some problems to understand what's going with IPv6.
So when I start the plugin my router reports a new device with an IPv4 and a link local IPv6. What is missing though is a global IPv6 and a hardware ID so that I can configure the ports on my router. The strange thing is, if I look at ifconfig inside the jail, it shows me a global IPv6. Even more strange is, that I can ping this IPv6 from every device in my network. However if I try to access nextcloud via this IP address, I get a timeout.
My questions are:
1. Why is there no global IPv6 and hardware id showing in my router?
2. Why can I ping the global IPv6 anyway?
3. What data can I post here to help you understand the problem?
4. What IPv6 addresses can I post here and what IPv6 addresses should I better not post publicly? I'm still a total IPv6 noob.