In your letter dated Tue, 8 Oct 2019 12:56:15 +0200 you wrote:
In the Netherlands, there is no mobile operator providing IPv6 connectivity. None! I cannot get IPv6 on my mobile connection!
KPN announced last week (September 30) that they started providing mobile customers with IPv6. They seem quite careful, so it may take a while before they enable it everywhere.
Also, in the Netherlands, the one Internet-to-home provider providing dual-stack IPv6 (w/o NAT mess) is being assimilated by it's parent who, after twenty-five years, is still technologically behind and can't deliver IPv6 themselves.
As far as I know, KPN does have some IPv6 on DSL. Both Ziggo and KPN provide IPv6 with some sort of carrier grade NAT for IPv4. But it should be easy enough to obtain real IPv4 elsewhere...