CONFIG_BUILTIN_DTB_SOURCE is not available for the selected architecture x86.
Result is shown for architecture riscv

Built-in device tree source

configname: CONFIG_BUILTIN_DTB_SOURCE

Linux Kernel Configuration
└─>Boot options
└─>Built-in device tree source
In linux kernel since version 3.10 (release Date: 2013-06-30)
DTS file path (without suffix, relative to arch/riscv/boot/dts)
for the DTS file that will be used to produce the DTB linked into the
kernel.