default or selected kernelversion does not have config value CONFIG_IPV6_ROUTE_FWMARK.
Result is shown for kernelversion 5.15.113
IPv6: use netfilter MARK value as routing key
configname: CONFIG_IPV6_ROUTE_FWMARK
Linux Kernel Configuration
└─>Networking
└─>Networking options
└─>IPv6: use netfilter MARK value as routing key
In linux kernel since version 2.6.19 (release Date: 2006-11-29)
If you say Y here, you will be able to specify different routes for
packets with different mark values (see iptables(8), MARK target).
packets with different mark values (see iptables(8), MARK target).