QUIC not running over IPv6? Or is it AdGuard Home?

Thank you NextDNS! QUIC is such a great performance contender beneath all encrypted other protocols and I have to thank you for supporting this very early!

Since I'v changed all my AdGuardHome services to QUIC, I came across that no endpoint on IPv6 is checking in to NextDNS. While still resolving to ipv6 adresses it's not a big deal, but I still would like to know, if this is happening because of NextDNS or AdGuard...  Question to the round: there are simply no other alternatives to test with or are they?

Thanks for any input!