default or selected kernelversion does not have config value CONFIG_ARCH_SUPPORTS_RT.
Result is shown for kernelversion 6.9.9

CONFIG_ARCH_SUPPORTS_RT (not configurable)

configname: CONFIG_ARCH_SUPPORTS_RT

Linux Kernel Configuration
└─>General architecture-dependent options
└─>ARCH_SUPPORTS_RT
In linux kernel since version 5.1 (release Date: 2019-05-05)  
is selected by
CONFIG_PREEMPT_RT