Postgres connection access denied on IPv6 address
The IPv6 addresses starting with fe80: are link-local addresses. They cannot be routed across different subnets or the internet. They are for communication between machines connected to the same LAN only. The link-local range is defined as fe80::/10. If you trust everybody on your local LAN then you could do

host  all  all  fe80::/10  trust


If you don't trust everybody on your local LAN then you probably want to use username+password protection:

host  all  all  fe80::/10  md5


When specifying md5 you are still using username+password protection, but the password is not transmitted in a readable format anymore. Since you're not trusting people on your local LAN you probably shouldn't send a snoopable password over the wire either.