New ISP for me, apparently using ipv6, but I don't fully understand ...

Your server has to have an IPv6 address in the first place, but it's the AAAA record that translates your.server.name to that IPv6 address.

There's nothing special to be done at an "ISP level" ... there either is such record for your domain name or not. What your ISP does is to give you an IPv6 address and thus the ability to connect to other sites that have IPv6 addresses.