default or selected kernelversion does not have config value CONFIG_NFT_CHAIN_ROUTE_IPV6.
Result is shown for kernelversion 6.9.9

IPv6 nf_tables route chain support

modulename: nft_chain_route_ipv6.ko

configname: CONFIG_NFT_CHAIN_ROUTE_IPV6

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Network packet filtering framework (Netfilter)
└─>The IPv6 protocol
└─>IPv6: Netfilter Configuration
└─>IPv6 nf_tables route chain support
In linux kernel since version 3.13 (release Date: 2014-01-19)  
This option enables the "route" chain for IPv6 in nf_tables. This
chain type is used to force packet re-routing after mangling header
fields such as the source, destination, flowlabel, hop-limit and
the packet mark.

source code: