default or selected kernelversion does not have config value CONFIG_NET_CLS_RSVP6.
Result is shown for kernelversion 6.6-rc5

IPv6 Resource Reservation Protocol (RSVP6)

modulename: cls_rsvp6.ko

configname: CONFIG_NET_CLS_RSVP6

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>QoS and/or fair queueing
└─>IPv6 Resource Reservation Protocol (RSVP6)
In linux kernel since version 2.6.12  
The Resource Reservation Protocol (RSVP) permits end systems to
request a minimum and maximum data flow rate for a connection; this
is important for real time data such as streaming sound or video.

Say Y here if you want to be able to classify outgoing packets based
on their RSVP requests and you are using the IPv6 protocol.

To compile this code as a module, choose M here: the
module will be called cls_rsvp6.

source code: