default or selected kernelversion does not have config value CONFIG_NF_FLOW_TABLE_IPV6.
Result is shown for kernelversion 6.9.9

Netfilter flow table IPv6 module

modulename: nf_flow_table_ipv6.ko

configname: CONFIG_NF_FLOW_TABLE_IPV6

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Network packet filtering framework (Netfilter)
└─>The IPv6 protocol
└─>IPv6: Netfilter Configuration
└─>Netfilter flow table IPv6 module
In linux kernel since version 4.2 (release Date: 2015-08-30)  
This option adds the flow table IPv6 support.

To compile it as a module, choose M here.

source code: