Static IPv6 are rare by default because computers for end users should use IPv6 privacy extensions. In Ubuntu 16.04 LTS timeframe privacy extension was still broken a bit, so it did not work on every network adapter. Nowadays it just works, unless a crazy network gives you only /128.
The whole address changes, but there's usually a prefix that doesn't change, e.g. /64.
Whitelisting the /64 is then equivalent to whitelisting a single IPv4 address with a NATted network behind it, although since ISPs may use different IPv6 prefix lengths it might not be easy for users to know what they should use.
("ip ad" etc show the current address with prefix.)
What? Germany is one of the most privacy-aware countries. So people should make some noise. Of course internet is still a bit new for all of us as the still-chancellor noted to too long ago... So technical incompetence does not surprise me. Vodafone prefers to make headlines with criminal sales practices.
I have no idea about Windows and MacOS.