CONFIG_ARTHUR is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_ARTHUR.
Result is shown for kernelversion 6.5.1

RISC OS personality

modulename: arthur.ko

configname: CONFIG_ARTHUR

Linux Kernel Configuration
└─>Userspace binary formats
└─>RISC OS personality
In linux kernel since version 2.6.12  
Say Y here to include the kernel code necessary if you want to run
Acorn RISC OS/Arthur binaries under Linux. This code is still very
experimental; if this sounds frightening, say N and sleep in peace.
You can also say M here to compile this support as a module (which
will be called arthur).

source code: