CONFIG_ARCH_A5K is not available for thedefaultarchitecture x86.
Result is shown for architecture arm26
default or selected kernelversion does not have config value CONFIG_ARCH_A5K.
Result is shown for kernelversion 5.4.123


configname: CONFIG_ARCH_A5K

Linux Kernel Configuration
└─>System Type
In linux kernel since version 2.6.12  
Say Y here to to support the Acorn A5000.

Linux can support the
internal IDE disk and CD-ROM interface, serial and parallel port,
and the floppy drive. Note that on some A5000s the floppy is
plugged into the wrong socket on the motherboard.