CONFIG_BFIN_IDLE_LED is not available for thedefaultarchitecture x86.
Result is shown for architecture blackfin
default or selected kernelversion does not have config value CONFIG_BFIN_IDLE_LED.
Result is shown for kernelversion 5.13-rc2

Enable System Load/Idle LED

configname: CONFIG_BFIN_IDLE_LED

Blackfin Kernel Configuration
└─>Blackfin Processor Options
└─>Board customizations
└─>Enable System Load/Idle LED
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
Blinks the LED you select when to determine kernel load.