CONFIG_BUILTIN_DTB_NAME is not available for thedefaultarchitecture x86.
Result is shown for architecture loongarch

Source file for built-in dtb

configname: CONFIG_BUILTIN_DTB_NAME

Linux Kernel Configuration
└─>Kernel type and options
└─>Source file for built-in dtb
In linux kernel since version 6.8 (release Date: 2024-03-10)  
Base name (without suffix, relative to arch/loongarch/boot/dts/)
for the DTS file that will be used to produce the DTB linked into
the kernel.