[LargoLasskhyfv]

I don't know exactly anymore, because I'm now with a different ISP which natively supports v6. So can't reproduce.

I mean I (probably) could, but don't want to, because now I have IPv4 via CGNAT, but not with a private IP, a public dynamic one probably shared with who knows how many others.

But I can use IPSEC/OpenVPN/Wireguard to somewhere else with that. Though my CPE supports GRE.

Anyways, there are large implementation differences in CGNAT from ISP to ISP and even different access technologies within the same.