default or selected kernelversion does not have config value CONFIG_NF_CONNTRACK_IPV6.
Result is shown for kernelversion 6.6.1

IPv6 connection tracking support

modulename: nf_conntrack_ipv6.ko

Linux Kernel Configuration
└─> Networking support
└─> Networking options
└─> Network packet filtering framework (Netfilter)
└─> The IPv6 protocol
└─> IPv6: Netfilter Configuration
└─> IPv6 connection tracking support

In linux kernel since version 2.6.15 (release Date: 2006-01-02)  

Connection tracking keeps a record of what packets have passed
through your machine, in order to figure out how they are related
into connections.

This is IPv6 support on Layer 3 independent connection tracking.
Layer 3 independent connection tracking is experimental scheme
which generalize ip_conntrack to support other layer 3 protocols.

To compile it as a module, choose M here. If unsure, say N.

source code: