default or selected kernelversion does not have config value CONFIG_SUNRPC_REGISTER_V4.
Result is shown for kernelversion 5.3.7
Register local RPC services via rpcbind v4 (EXPERIMENTAL)
configname: CONFIG_SUNRPC_REGISTER_V4
Linux Kernel Configuration
└─>File systems
└─>Network File Systems
└─>Register local RPC services via rpcbind v4 (EXPERIMENTAL)
In linux kernel since version 2.6.28 (release Date: 2008-12-24)
Sun added support for registering RPC services at an IPv6
address by creating two new versions of the rpcbind protocol
(RFC 1833).
This option enables support in the kernel RPC server for
registering kernel RPC services via version 4 of the rpcbind
protocol. If you enable this option, you must run a portmapper
daemon that supports rpcbind protocol version 4.
Serving NFS over IPv6 from knfsd (the kernel's NFS server)
requires that you enable this option and use a portmapper that
supports rpcbind version 4.
If unsure, say N to get traditional behavior (register kernel
RPC services using only rpcbind version 2). Distributions
using the legacy Linux portmapper daemon must say N here.
address by creating two new versions of the rpcbind protocol
(RFC 1833).
This option enables support in the kernel RPC server for
registering kernel RPC services via version 4 of the rpcbind
protocol. If you enable this option, you must run a portmapper
daemon that supports rpcbind protocol version 4.
Serving NFS over IPv6 from knfsd (the kernel's NFS server)
requires that you enable this option and use a portmapper that
supports rpcbind version 4.
If unsure, say N to get traditional behavior (register kernel
RPC services using only rpcbind version 2). Distributions
using the legacy Linux portmapper daemon must say N here.