CONFIG_CMDLINE is not available for the selected architecture x86.
Result is shown for architecture loongarch

Built-in kernel command line

configname: CONFIG_CMDLINE

Linux Kernel Configuration
└─>Kernel type and options
└─>Built-in kernel command line
In linux kernel since version 2.6.12 )
For most platforms, the arguments for the kernel's command line
are provided at run-time, during boot. However, there are cases
where either no arguments are being provided or the provided
arguments are insufficient or even invalid.

When that occurs, it is possible to define a built-in command
line here and choose how the kernel should use it later on.