in m limited sample size of one avm fritz.box, yes. What ivp6 address did you use to try and connect? a device typically has multiple - i.e. dont use fd00::, fe80::

port forwarding in your router properly set up?

i’ve been on CGNAT and just pointed my domain to my ipv6 address with no issues - every isp should hand out huge v6 subnets dedicated to you.

Since my v6 prefix is not stable, i use ddclient from my homeserver to update my domains AAAA record