Not sure why thats the case for you. I'm on Vodafone/Kabel Deutschland too and got full ipv4/ipv6 dual stack? Is that one of those regional limitations that Vodafone seems to have?
Oftentimes you can just ask the customer service of Vodafone. If you reach a good agent, they will switch you away from CGNAT and you get a proper /56 public routable prefix on your cable line. Also works great for me. Be aware, the Vodafone modem won‘t forward the prefix for you. Use a Fritzbox or one of the other few cable modems where you get full control.
What everyone seems to be missing here is that in France alot of heating during winter is done with electricity which is not the case in germany.
So peak electricity usage in France during Winter is much higher and that is the time where it needs to import alot.