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

Real-time Clock

configname: CONFIG_UML_REAL_TIME_CLOCK

Linux/Usermode Kernel Configuration
└─>UML-specific options
└─>Real-time Clock
In linux kernel since version 2.6.12  
This option makes UML time deltas match wall clock deltas. This should
normally be enabled. The exception would be if you are debugging with
UML and spend long times with UML stopped at a breakpoint. In this
case, when UML is restarted, it will call the timer enough times to make
up for the time spent at the breakpoint. This could result in a
noticable lag. If this is a problem, then disable this option.