CONFIG_HOST_2G_2G is not available for thedefaultarchitecture x86.
Result is shown for architecture um
default or selected kernelversion does not have config value CONFIG_HOST_2G_2G.
Result is shown for kernelversion 5.4.123

2G/2G host address space split

configname: CONFIG_HOST_2G_2G

Linux/Usermode Kernel Configuration
└─>UML-specific options
└─>2G/2G host address space split
In linux kernel since version 2.6.12  
This is needed when the host on which you run has a 2G/2G memory
split, instead of the customary 3G/1G.

Note that to enable such a host
configuration, which makes sense only in some cases, you need special
host patches.

So, if you do not know what to do here, say 'N'.