CONFIG_GDBSTUB is not available for thedefaultarchitecture x86.
Result is shown for architecture frv
default or selected kernelversion does not have config value CONFIG_GDBSTUB.
Result is shown for kernelversion 6.7-rc3

Remote GDB kernel debugging

modulename: gdb-stub.ko

configname: CONFIG_GDBSTUB

Linux Kernel Configuration
└─>Kernel hacking
└─>Remote GDB kernel debugging
In linux kernel since version 2.6.12  
If you say Y here, it will be possible to remotely debug the kernel
using gdb. This enlarges your kernel ELF image disk size by several
megabytes and requires a machine with more than 16 MB, better 32 MB
RAM to avoid excessive linking time. This is only useful for kernel
hackers. If unsure, say N.

source code: