default or selected kernelversion does not have config value CONFIG_IP6_NF_TARGET_MARK.
Result is shown for kernelversion 5.4.123

MARK target support

modulename: ip6t_MARK.ko


Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Network packet filtering (replaces ipchains)
└─>IPv6: Netfilter Configuration (EXPERIMENTAL)
└─>MARK target support
In linux kernel since version 2.6.12  
This option adds a `MARK' target, which allows you to create rules
in the `mangle' table which alter the netfilter mark (nfmark) field
associated with the packet packet prior to routing. This can change
the routing method (see `Use netfilter MARK value as routing
key') and can also be used by other subsystems to change their

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

source code: