I provisioned a machine on Hetzner Cloud. All default settings except Networking where I chose ONLY IPv6. Added an SSH key too.
When I try to connect over ssh, I get the following error:
The public address given by hetzner was 2a01:4ff:1f0:c2f8::/64, but I saw online that I have to replace the /64 with 1.

2a01:4ff:1f0:c2f8::/64is the whole subnet, your server will have one (or more) addresses in that subnet. This could be2a01:4ff:1f0:c2f8::1, but could also be a randomly generated suffix.