"Unknown error occurred" when trying to add Apple iCloud Integration

This seems to be an IPv6 issue but you have to connect to the host system and not the containerized hosted HA. I fixed this from this thread: Unable to reach the home assistant cloud - Nabu Casa

# Change as your network requires
ssh -p 22222 [email protected]
nmcli con show
# Note down the NAMES of the connections you have and substitute with the ones in quotes
nmcli con modify "Wired connection 1" ipv6.method disabled
nmcli con modify "my-network" ipv6.method disabled