TIL that #simyo (mobile provider) actually supports #ipv6 on their network, but it does not seem to be enabled by default in the APN config (which lives on the SIM, right?).
This 4y old forum thread (https://forum.simyo.nl/internet-4g-en-5g-62/wat-is-de-status-van-de-ipv6-uitrol-44316) said the same, assuming it was only enabled for new customers, but I only subscribed a few months ago.
To enable ipv6 on Simyo: Settings -> Network & Internet -> SIMs -> Select SIM -> Access Point Names -> Select APN -> APN (roaming) protocol: IPV4/IPV6. Then reboot.
Edited 20d ago